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Program ASTROCLK Astronomical Clock and Celestial Tracking Program with Celestial Navigation (C) Copyright 1988-1991, All Rights Reserved by David H. Ransom, Jr. Rancho Palos Verdes, CA Version 9117 April 22, 1991 ASTROCLK Astronomical Clock and Celestial Tracking Program Page i TABLE OF CONTENTS ACKNOWLEDGEMENTS.........................................1 INTRODUCTION.............................................2 HARDWARE REQUIREMENTS....................................7 PROGRAM OPERATION........................................9 Required ASTROCLK Files...............................9 ASTROCLK Source Files ................................10 Starting Program ASTROCLK.............................11 Running Program ASTROCLK..............................13 FUNCTION KEYS AND HELP...................................17 F1 Display HELP Screens...............................17 F2 Display Target Object EPHEMERIS....................17 F3 Set Time and/or Date...............................17 Read Hardware Clock................................18 Set ALARM or INTERVAL TIMER Time...................18 F4 Toggle Clocks ON or OFF............................18 Enable Simulated Real Time.........................18 F5 Set Target Coordinates.............................19 Enter USNO Star Name or Number.....................19 Search for Nearest USNO Star.......................19 Search EXTERNAL STAR CATALOG by Name or ID.........19 Search EXTERNAL STAR CATALOG by RA and DEC.........20 Search EXTERNAL STAR CATALOG for Nearest Star......20 Manual Target Data Entry...........................20 Set Polaris Coordinates............................22 F6 Set Local Coordinates..............................22 Set Destination Coordinates........................22 Set Local Conditions...............................22 F7 Set Display Format.................................22 Change Target Display Coordinates..................23 F8 Precess Internal Star Database.....................23 F9 DOS Shell..........................................24 Execute Preset DOS Command.........................24 Execute USNO Ephemeris (ICE or FA).................24 F10 Celestial Navigation...............................25 Setting Program Options............................25 0-9 Select Display Window Mode.........................25 SETTING PROGRAM OPTIONS..................................27 Setting the DAYLIGHT FLAG.............................27 Setting the ZONE CORRECTION...........................28 Setting the COLOR FLAG................................29 Setting the ICE/FA FLAG...............................29 Setting the CALENDAR FLAG.............................30 Setting the FILE NAMES and PATHS......................30 Setting the PRESET DOS COMMAND........................33 SETTING LOCAL/UT/TDT TIME AND DATE.......................34 Setting the LOCAL/UT/TDT Time.........................36 Setting the LOCAL/UT Date.............................37 Setting the time/date from NIST/USNO .................39 SETTING LOCAL AND DESTINATION COORDINATES................41 SETTING LOCAL CONDITIONS.................................44 ASTROCLK Astronomical Clock and Celestial Tracking Program Page ii DUAL-TIME DISPLAYS.......................................45 JULIAN DATE INFORMATION..................................47 ALARM AND INTERVAL TIMER OPERATIONS......................48 Using the ALARM Function..............................48 Using the INTERVAL TIMER..............................49 Linked ALARM & INTERVAL TIMER Operation...............50 TARGET TRACKING DISPLAY..................................51 TARGET OBJECT EPHEMERIS..................................55 PRECISION TIME AND DATA DISPLAYS.........................57 Precision Time Display #1.............................58 Precision Time Display #2.............................59 Precision Data Display #1.............................60 Precision Data Display #2.............................60 Precision Data Display #3.............................61 Solar Rise/Set & Twilight.............................61 PLANETARY DATA DISPLAYS..................................63 MINOR PLANET SELECTION...................................67 Entering Orbital Parameters...........................70 CELESTIAL NAVIGATION.....................................72 Setting UT TIME ZONE OFFSET...........................73 Navigation by Dead Reckoning..........................76 Celestial Navigation with Star Sights.................83 Selecting USNO Navigational Stars.....................87 Celestial Navigation Example..........................89 SIDEREAL TIME AND EQUATORIAL COORDINATES.................94 USNO COMPUTER EPHEMERIS PROGRAMS, ICE AND FA.............96 USNO STANDARD NAVIGATIONAL STARS.........................99 CONSTELLATIONS AND NAMES.................................101 EXTERNAL STAR CATALOGS ..................................105 USNO Star Catalogs ....................................105 Sky Catalogue 2000.0 ..................................106 External Catalog Searches .............................106 PRECESSION AND STELLAR MOTION............................109 DATES AND THE GREGORIAN CALENDAR.........................111 WHAT TIME IS IT?.........................................118 PRECISION AND ACCURACY TESTS.............................125 Compiler..............................................125 Calendar Dates........................................126 Julian Dates..........................................127 Universal Times (UT and UTC)..........................127 Terrestrial Dynamical Time (TDT, ET and Delta-T)......127 Atomic Times (TAI and A.1)............................128 Sidereal Times (GMST and GAST)........................128 Precession............................................129 Solar Position Calculations...........................131 Major Planet Position Calculations....................134 Minor Planet Position Calculations....................135 Celestial Navigation Calculations.....................135 J2000.0 Internal Star Database........................137 ASTROCLK MESSAGES AND ERRORS.............................138 ASTROCLK Numbered Errors and Cautions.................138 Other ASTROCLK, QuickBASIC and DOS Errors.............145 A BRIEF EDITORIAL........................................147 BIBLIOGRAPHY.............................................149 ASTROCLK Astronomical Clock and Celestial Tracking Program Page 1 ACKNOWLEDGEMENTS Few tasks of any consequence are accomplished unaided. For ASTROCLK, in addition to the numerous references cited in the BIBLIOGRAPHY, there are several individuals to whom special thanks are due. Ward Harman, a retired engineer living near me in Palos Verdes, California, has spent many hours testing and validating the performance of various aspects of ASTROCLK, advising me of errors when he found them, and making numerous suggestions with respect to both style and substance. Steve Brewster, of Stony Ridge Observatory high above Pasadena, California, has been most generous with his time, advice, and encouragement. To all of that, he added a long and fascinating evening at the Observatory where we were able to experience firsthand the thrill of "real" astronomy using SRO's 30-inch reflector and which helped me to better understand how ASTROCLK might better be used in that environment. Special thanks to Captain Helge Brudvik of the Royal Viking Sky for the freedom of the bridge, and to Chief Officer Magnus Bakken for his practical demonstrations of navigation at sea (as well as many hours of pleasant conversation). Many of ASTROCLK's navigation functions were tested and verified during a ten week cruise around South America in early 1990. And to all of those astronomy and computer enthusiasts who have called, written, or left messages on my bulletin board system, my thanks for your kind words and suggestions. Those letters and calls inform me that ASTROCLK is being used in Australia, Denmark, England, Finland, France, Hong Kong, Israel, Italy, Japan, Sweden, Taiwan, and the Virgin Islands in addition to the United States and Canada. I must be doing something right! ASTROCLK is now embarking upon its third year. Finally, and by no means least, my wife Vicki has been both patient and supportive during the many hundreds of hours I have spent hunched over one or another of my computers as ASTROCLK has evolved from a simple sidereal clock to the complex program it is today. It was her interest in, and curiousity about, astronomy and the night sky which helped inspire my efforts in the first place, and her encouragement has been essential during the years that I have invested in ASTROCLK. April 1991 David H. Ransom, Jr. Rancho Palos Verdes, CA ASTROCLK Astronomical Clock and Celestial Tracking Program Page 2 INTRODUCTION Program ASTROCLK is an Astronomical Clock and Celestial Tracking Program. ASTROCLK is copyrighted software; you are granted a non-exclusive limited license for non-commercial use. If you wish to use ASTROCLK commercially, write for license information. Registration of your copy of ASTROCLK will be appreciated but is not required. See the file REGISTER for registration instructions and information. Use ASTROCLK if you like it, discard it if you don't. There are no warranties of any kind. For information on how to obtain the current version of the program, see the section A BRIEF EDITORIAL. And now, on with the story ... Like many people, I have long been fascinated by the stars at night and by things astronomical. But it was not until some years ago, when I spent considerable time in the foothills of Northern California, that I regularly saw the night sky without the interference of city lights. There followed a heightened interest in the stars and a desire to be able to recognize the various constellations and important individual stars. Many books, star charts, and cold winter nights later the age of the Personal Computer dawned. Suddenly, I realized, I had a tool which would enable me to figure out many of these things on my own and practically in real time. Program ASTROCLK has evolved from a series of smaller programs, each designed to calculate some little piece of astronomical data which I wanted. Each time that I needed still another bit of data in order to do something, I'd search out the necessary formulae or methods and write a new little program to automate the process. After a relatively short period of time I discovered that I had literally dozens of such small programs, but no single program was ever sufficient to get me all the information I sought at a particular time. Equally frustrating, none of the stand-alone programs available or that I had written up to that point gave me the information in real time, adjusted for my geographical location. I always had to look up something I'd forgotten and run a number of programs to get the data I wanted. And to further complicate things, there are an almost unbelievable number of different methods for telling time, of which perhaps half a dozen or so are useful to the casual astronomer or navigator. I finally mastered the zone changes from Greenwich to Los Angeles, but converting local time to sidereal time ("star time", if you prefer) in my head has so far eluded me. Program ASTROCLK was intended to solve all of these problems for me. While it is still some distance from accomplishing that rather ambitious goal, it's a very big step along the way. I'm starting to run out of "necessary" features to add! As with any profession, astronomers and navigators have developed a technical language all their own to describe the phenomenae of time and celestial mechanics. Not only is this language almost as complex as the science it seeks to describe, but many seemingly common words carry definitions far divorced from everyday life and our intuitive understanding of their ASTROCLK Astronomical Clock and Celestial Tracking Program Page 3 meaning. The amateur astronomer or layman can easily become hopelessly confused, particularly as not all texts, organizations, and related professions necessarily use precisely the same words or even the same definitions to describe a given measurement or item of data. All too frequently the definitions have changed over time, and sometimes they are even reversed from one discipline to another. For my own understanding and entertainment, I have spent considerable time researching the subject and attempting to assemble a consistent set of computer programs and algorithms to facilitate the practical use of my personal computers in astronomy and navigation. Program ASTROCLK now represents a continuing effort spanning more than three years and two thousand hours of work. I hope that effort is judged worthwhile. The advent of the truly portable personal computer has served as an additional spur to these efforts so that I may have the information at my fingertips no matter where I may travel. There are moments when I wonder who is the master and who the slave. I have used many and varied sources and have made every effort to assure the consistency and accuracy of the information and calculations presented. However, I alone am responsible for the final outcome -- along with any errors that may be discovered. My thanks to those individuals who have taken the time to report problems and suggest improvements. Without their interest and encouragement, I doubt that ASTROCLK would have become what it is or that my efforts would have continued. The first and most important order of business for any astronomer or navigator is to know what time it is. For ASTROCLK, I assume that the computer's internal clock has been set to the correct local time, keeps reasonably good time, and that the relationship between local time and Coordinated Universal Time can be calculated or is known. To a high degree of accuracy, what is now known as Coordinated Universal Time (UTC) was previously called Greenwich Mean Time (GMT); there are those who still insist on using the old name. The U. S. military forces, ever adept at finding a different name for things we might otherwise recognize, refer to UTC as Zulu Time. In the United States, the National Bureau of Standards continuously broadcasts UTC on stations WWV (Fort Collins, Colorado) and WWVH (Kauai, Hawaii); the frequencies transmitted are: 2.5MHz, 5MHz, 10MHz, 15MHz and 20MHz (WWV only). Reception will vary depending upon the time of day, geographic location, and current atmospheric conditions. In Europe and in many places around the world, the BBC World Service gives a time signal every hour which is synchronized with Greenwich Mean Time, essentially identical with UTC. As an aside, I have noticed that the hardware clocks in my computers maintain more accurate time than do the software clocks (particularly with versions of MS-DOS prior to 3.xx). However, the accuracy of the hardware clock can vary substantially from one system to the next, even when using identical software. Further, some programs which use local area networks or high speed serial communications may disable the software clock during operation and the time errors can become substantial. Other ASTROCLK Astronomical Clock and Celestial Tracking Program Page 4 software can also suspend timekeeping functions for brief intervals. For example, use of the program BROOKLYN BRIDGE (inter-computer communications) can introduce errors of tens of seconds or more. I recommend that you first check the accuracy of your software clock, the one that keeps track of time after you begin using the computer, over a period of several hours. An easy way to do this is simply to run ASTROCLK for several hours and observe the displayed time compared to an accurate clock or watch. Second, if you temporarily leave ASTROCLK using Function Key F9, note the time when you return to ASTROCLK and, if the time is in error, make a note of what programs or operations in your system affect the accuracy of the software clock. In either case, reset your software clock from time to time if necessary or, if your computer has an accurate hardware clock, re-read your hardware clock to take advantage of its superior accuracy. For many computers, ASTROCLK can do this using Function Key ALT-F3. Using this more or less accurate time standard, ASTROCLK displays the current Local Time and Local Date, the Local Mean Sidereal Time ("star time"), and the Local Mean Solar Time (referred to the local longitude). Also shown are: Coordinated Universal Time (UTC) which, for years 1925 and later and to the accuracy used here, is the same as Greenwich Mean Time (GMT); the UTC Date at the Prime Meridian (Greenwich, longitude 0 degrees); Greenwich Mean Sidereal Time; and, the local time zone relative to UTC. All times are in 24-hour notation and local time is Local Standard Time or Local Daylight Time, depending upon the setting of the DAYLIGHT FLAG. If your time zone is offset from the computed local time zone, see also the section SETTING PROGRAM OPTIONS. Note that dates are shown as DD-MM-YYYY (European style, day-month-year) and that because of the time span covered the full 4-digit year is required. Any one of the times may be displayed in a main window with extra large digits for easy visibility. Precision Time and Data Displays are available which show a variety of common time standards to a precision of 0.0001 seconds along with other astronomical information. The display is updated each second -- provided the computer can make the necessary calculations in that time. If the clocks are stopped, the user may enter any desired time and date and view the calculated values for all of these items to a high degree of accuracy. The values have been carefully checked against the Astronomical Almanac, prepared each year jointly by the U. S. Naval Observatory (USNO) and the Royal Greenwich Observatory, and the USNO Interactive Computer Ephemeris (ICE) and are believed accurate to plus or minus 0.01 seconds or better; note that the displayed precision is 0.0001 seconds. Initially, the program assumes the geographical location of Rancho Palos Verdes, California, near Los Angeles. However, an auxiliary file contains the names and locations of a number of cities which can quickly be read by ASTROCLK. The file may easily be edited to include your favorite locations and their coordinates. ASTROCLK saves these data (and others) in a special file, ASTROCLK.INI, and the new place name and coordinates will be automatically loaded when the program is next started. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 5 A tracking feature is included which allows the user to continuously display the celestial and horizon (observer) coordinates for the pole star, Polaris, and the 57 stars designated by the U. S. Naval Observatory (USNO) as "Standard Navigational Stars". Data for these stars are preset in the program and are for Epoch J2000.0, the current standard epoch for celestial coordinates. The list of these standard stars is from USNO, and the actual coordinates have been taken from the USNO Floppy Almanac 1988. The data for proper motion is also included for the correct calculation of precession. ASTROCLK includes orbital and position formulae for each of the major planets to enable the user to select a desired planet and view its position. The user may also select a minor planet; the supplied catalog, ASTROCLK.MPC, contains the first 250 minor planets. The full minor planet catalog currently contains 4000 entries and is available on my bulletin board system. Alternatively, the user may search an external star catalog for a desired star using the catalog number or any of several star names. The supplied catalog, ASTROCLK.CC1, contains 1644 stars and objects whose coordinates have been calculated by USNO and which are also for Epoch J2000.0. Finally, the user may manually enter the celestial coordinates (right ascension and declination) for a star, planet, or other object. Once the celestial coordinates have been selected or entered, ASTROCLK continually displays the local ("observer" or "horizon") coordinates as well as the Sidereal Hour Angle (SHA, preferred by navigators), computed once per second. The program also displays coordinates adjusted for atmospheric refraction, important as an object approaches the horizon. Using a small portable computer, the would-be stargazer may take the program into the field and use it to locate and track the desired object. The user may also enter the local horizon coordinates, Altitude and Azimuth, for a bright star and ask ASTROCLK to select the USNO Standard Navigational Star which is closest to the position entered at that time. It will also find Polaris if the coordinates are close enough, but the algorithm for star selection is less accurate near the poles. The same process may be used with the external star catalog. So the program works both ways: it can tell you where to look for a selected star or, if you tell it where you see a star, it can tell you which star you are probably looking at. By stopping the real time clock and entering a date and time of choice, the user may also determine the position of a celestial object at any time in the past or future. However, since some formulae and star coordinates assume the present epoch, J2000.0 usually, the accuracy of positions calculated may decrease for epochs distant from modern times. A simulation mode may be used to view data in simulated real time at any preset time and date. Inspired by several long sea journeys, ASTROCLK can perform a number of navigational functions, including dead reckoning and celestial navigation. The dead reckoning process yields results as accurate as the information supplied. For celestial navigation the accuracy is not quite as high as can be achieved with the Nautical Almanac (and a lot of tiresome calculations) or by ASTROCLK Astronomical Clock and Celestial Tracking Program Page 6 sophisticated satellite navigation systems; with "perfect" star sights, ASTROCLK's celestial navigation is accurate to approximately 0.25 nautical miles. Great circle distance calculations have been carefully checked against the satellite navigation system on board the Royal Viking Sky and ASTROCLK's results agree to within approximately 0.25 nautical miles for targets/waypoints as distant as one thousand nautical miles. ASTROCLK includes a perpetual calendar which will display any month of any year from -4713 B.C. into the future. The default calendar algorithms follow the Julian Calendar from -4713 B.C. until October 4, 1582 after which the Gregorian Calendar is used. This follows civil usage in catholic countries as well as astronomical convention, but will not correspond to the date convention used in countries which did not adopt the Gregorian Calendar in 1582. Great Britain and its colonies (including what is now the United States), for example, did not adopt the Gregorian Calendar until September 2, 1752. Dates prior to the introduction of the Julian Calendar in 46 A.D. are in accordance with the Julian Proleptic Calendar (the Julian Calendar extended backwards in time from 46 A.D.) and are therefore more or less a figment of the program's imagination; the dates computed are consistent with that calendar (and astronomical convention) but bear no relation to any calendar in actual use at the time. A program option is available to choose between the strict Julian calendar and either the 1582 or the 1752 adoption of the Gregorian calendar. An additional date display is also available which shows several styles of Julian Date, the local date, the current day of the year, and the day of the week. ASTROCLK is presently being used at several observatories for both time and tracking displays. For night use, the display may be set to the RED mode; the monitor intensity may then be adjusted for best comfort and protection of night vision. A GREEN mode is also available which may reduce eye fatigue during periods of extended use. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 7 HARDWARE REQUIREMENTS ASTROCLK was designed for and is best operated using a color adapter and color monitor, CGA/EGA/VGA. The program can be forced to emulate monochrome output on color video adapters with the "/M" command line option. Tests on monochrome systems such as HGC (true monochrome adapter and display, as opposed to a system using a monochrome display on a color-compatible adapter), have been successful when used with the "/M" command line option. The program has been used on a wide variety of IBM-compatible systems with few if any problems. Users have reported successful operation on high speed systems including an IBM PS/2 Model 80 and a Compaq Model 386/20. The program has also been tested on various "IBM-clone" systems with numerous variations including CGA/EGA/VGA Graphics Adapters and Hercules Graphics Adapters (HGC). The only problems have been with "strange" BIOS implementations on certain clone systems (for example, one Leading Edge system failed to execute but another executed properly) and occasional TSR's (Terminate and Stay Resident programs) which refuse to cooperate properly. There is no cure for BIOS problems but removal of TSR's will usually cure those problems. Several ASTROCLK functions use the QuickBASIC SHELL command to execute DOS commands directly or to return the user to a secondary command processor (Function Key F9). All of my systems use MS-DOS Version 3.1 or higher but I have read reports that the QuickBASIC SHELL does not operate correctly for versions of MS-DOS or PC-DOS of 3.0 or lower. I recommend that you upgrade to Version 3.2 or higher for better system performance in general and to avoid problems with the SHELL command in particular. ASTROCLK supports the EGA 43-line and VGA 50-line modes to a limited extent: if the system is in that mode at program startup, it will return to that mode upon final exit. I'm rather fond of the EGA's 35-line mode and often use it in preference to either 25- or 43-line modes. Unfortunately for me, QuickBASIC (any version) refuses to recognize the 35-line mode on entry and returns the system to the 25-line mode upon exit. Regardless of the screen mode detected at the start of execution, ASTROCLK always sets the system to 80 columns and 25 lines for maximum compatibility and ease of viewing. The "/M" command line option (see PROGRAM OPERATION, below) is recommended for systems equipped with a monochrome display adapter and monochrome monitor. It also forces monochrome display on computers which have color-compatible video adapters but simulate colors with shades of gray or varying intensities of a single color. When "/M" is used with a color adapter and monitor, the display will be white on black background. Results may vary from system to system. The performance of different computers varies considerably, the single most important factor being the presence or absence of a math coprocessor. Program ASTROCLK uses the double precision floating point format for almost all calculations, and the added performance of a coprocessor is significant. Without it, even an AT-class computer has perceptible computation delays; with it, an ASTROCLK Astronomical Clock and Celestial Tracking Program Page 8 old PC-class computer easily completes the same tasks within one second. I have not tested the minimum memory requirements for ASTROCLK. All of my systems are equipped with 640K. As of Version 8907, the program requires more than 200K bytes of memory and probably WILL NOT execute in a minimum 256K system. Since ASTROCLK can invoke QuickBASIC's SHELL command to return you temporarily to DOS with ASTROCLK still in memory, I recommend the use of 640K memory. However, even with 640K of memory, the fact that ASTROCLK is resident means that programs which require a great deal of memory may fail to execute properly under the shell. These programs must be executed outside ASTROCLK. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 9 PROGRAM OPERATION This section describes the operation of program ASTROCLK, including required files, starting the program, and initial operations. Required ASTROCLK Files Program ASTROCLK is normally distributed in archived form and includes the following files: Main ASTROCLK Program --------------------- ASTROCLK.EXE Executable ASTROCLK program ASTROHLP.EXE Executable ASTROHLP program ASTROCLK Documentation ---------------------- ASTROCLK.DOC ASTROCLK Documentation Description ASTROCLK.DC1 ASTROCLK Documentation, Part I ASTROCLK.DC2 ASTROCLK Documentation, Part II ASTROCLK.HST Revision history for ASTROCLK ASTROCLK.NEW Recent revision history ASTROCLK Support Files ---------------------- ASTROCLK.CC1 Data file of additional stars ASTROCLK.CTY Data file of cities/locations ASTROCLK.INI * Data file for initialization ASTROCLK.MPC Minor Planet Catalog ASTROFNT.COM EGA Soft Font (EXPERIMENTAL) MESSIER.CC1 Data file of Messier objects only REGISTER Program registration information * May not be present in distribution files Program ASTROCLK is usually distributed via bulletin board systems as two compressed files. A complete version should contain ALL of the listed files except as noted. Depending upon the source, different file compression programs may be required to unpack the files; the required program is usually indicated by the filetype of the archived files. Only the files ASTROCLK.EXE and ASTROHLP.EXE are required for operation of the program. If necessary, file ASTROHLP.EXE may be omitted but the on-screen help functions will not operate and no warning message will be given. File ASTROCLK.CTY adds the capability to read the location of various U. S. and and international cities; a warning message is displayed if it is not present and a search of the file is attempted. NOTE: The format of the .CTY files changed with Version 9050, adding elevation. Old .CTY files must be edited to add the elevation in meters (or add a comma followed by a zero) ASTROCLK Astronomical Clock and Celestial Tracking Program Page 10 using any ASCII text editor. File ASTROCLK.CC1 contains data for 1644 stars and galaxies which may be requested by name or number; a warning message is displayed if the file is not present and a catalog search is requested. File ASTROCLK.INI is not normally included; it is quite small and will be created automatically. An additional catalog file, MESSIER.CC1, contains data for the 108 Messier objects which have been extracted from file ASTROCLK.CC1, for convenience in locating these objects. Messier objects are commonly referred to by "M" numbers such as M3 or M11; there is no Messier object M40. ASTROCLK can also process and track minor planets and asteroids. File ASTROCLK.MPC is an external binary catalog containing the first 250 minor planets which may be selected by Minor Planet Number or Name. The binary catalog has been prepared with my program MPCAT, developed for this purpose, using data compiled by E. G. Bowell of the Lowell Observatory. The full minor planet catalog, currently EPHEM892.MPC with 4,000 minor planets listed, is available separately from my bulletin board system. New updated minor planet catalogs are released at approximately six month intervals. These versions of the minor planet data have been converted into the binary format expected by ASTROCLK using program MPCAT; as with program ASTROCLK, the current version of MPCAT and the source are always available from my bulletin board system (BBS). See the section A BRIEF EDITORIAL for more information on the BBS. As an experiment for EGA and VGA users, file ASTROFNT.COM provides an alternate screen font. The screen typeface is changed from its normal appearance to a cleaner typeface resembling Helvetica. To use this screen font, enter "ASTROFNT" prior to executing program ASTROCLK or press the letter "E" during normal operation. CAUTION: Use of ASTROFNT with other display adapters may produce unpredictable results! ASTROCLK Source Files --------------------- The following source files are required to compile program ASTROCLK. These files are available ONLY with program registra- tion. See the file REGISTER for registration information and instructions. ASTROCLK.MAK Source module list ASTROCLK.BAS Main ASTROCLK source ASTROCLK.INC Common $INCLUDE file ASTROSB1.BAS SUB/FUNCTION source, 1/4 ASTROSB2.BAS SUB/FUNCTION source, 2/4 ASTROSB3.BAS SUB/FUNCTION source, 3/4 ASTROSB4.BAS SUB/FUNCTION source, 4/4 ASTROHLP.BAS Source for ASTROHLP ASTROCLK is written and compiled using Microsoft QuickBASIC Version 4.50 or Microsoft BASIC Compiler Version 7.1. In addition to the .BAS source files, ASTROCLK.INC contains DIM, COMMON, and ASTROCLK Astronomical Clock and Celestial Tracking Program Page 11 CONST statements required by the other source modules. The file ASTROCLK.MAK is required for use in the interpreter mode. Al- though I normally compile and link using the BASIC Compiler, the following batch file may be used to compile and link ASTROCLK with QuickBASIC 4.50 to produce the two required .EXE files (all files assumed in the current drive and directory): bc astroclk/e/x/o/t/c:512; bc astrosb1/o/t/c:512; bc astrosb2/o/t/c:512; bc astrosb3/o/t/c:512; bc astrosb4/o/t/c:512; link /ex astroclk+astrosb1+astrosb2+astrosb3+astrosb4, astroclk.exe; bc astrohlp/e/x/o/t/c:512 link /ex astrohlp,astrohlp.exe; The on-line help functions for ASTROCLK are contained in a separate program, ASTROHLP.EXE, automatically executed by Function Key F1. The source file for help is ASTROHLP.BAS. Note that the compile and link commands may be particular to the versions of BC and LINK being used, Version 4.50 and Version 3.69 respectively in this case. See A BRIEF EDITORIAL near the end of this document and file REGISTER for information on how to obtain the most recent version of all ASTROCLK files. Users who require minimum size run files because of memory constraints may choose to compile and link ASTROCLK to use Microsoft's runtime module, BRUN45.EXE, instead of generating a standalone program. Approximately 40K less RAM memory is required for ASTROCLK in this configuration. However, this configuration is less flexible with respect to starting directory: BRUN45.EXE must be in the same directory as ASTROCLK.EXE, and ASTROCLK must be run from that directory. Batch files which work correctly with the standalone version may have to be modified. Starting Program ASTROCLK To start ASTROCLK, first verify that your computer is set to the correct local time and date using the TIME and DATE commands, then change to the subdirectory containing the ASTROCLK files and enter one of the following commands at the DOS prompt: ASTROCLK [for all COLOR monitors] ASTROCLK /M [for MONOCHROME monitors] ASTROCLK /R [to force RED on color monitors] ASTROCLK /G [to force GREEN on color monitors] followed by RETURN (or ENTER, which I will call RETURN) and the program will begin execution. The descriptions and examples in this documentation assume you are using a color monitor; if you ASTROCLK Astronomical Clock and Celestial Tracking Program Page 12 are using a monochrome monitor, ignore all references to colors. However, all users should note that negative years, described as RED in this documentation, will BLINK in the program's date windows when the "/M" option is used or when either of the single color program modes is set; the UTC Julian Date window, of course, will show the correct number for all dates. Using one of the command line color options forces the program to that color mode immediately and overrides any prior color mode. When a color option is NOT given, ASTROCLK will initially display its signon screen in full color (for color monitors); using the "/R" or "/G" color option will use the selected color for the signon screen as well as all subsequent operations. This is particularly useful with the RED option to protect night vision when alternating between ASTROCLK and other programs. ASTROCLK may also be switched between the monochrome, color, red, and green modes during execution using Function Key ALT-F10. See the section SETTING PROGRAM OPTIONS for further information. As initially configured, ASTROCLK assumes that the all data files are in the current drive and directory. If this is not the case, you may include the drive and path for the various ASTROCLK data files using the following command pattern (note space after ASTROCLK): ASTROCLK [drive:][\path][coloroption] "drive:" must be a single letter followed by a colon and must correspond to a valid drive. If no path is included, ASTROCLK assumes the current directory on the specified drive or, if no drive is included, on the current drive. If the path is included, it must begin with the backslash, "\", and the path must exist. See your DOS manual for an explanation of paths and directories. If present, the color option must follow the drive and/or path; only ONE of the color options /M, /R, or /G may be used to force MONOCHROME, RED or GREEN respectively. Using a color option will override any prior color setting saved in file ASTROCLK.INI. If no color option is included on the command line, ASTROCLK will start in full color, then read the file ASTROCLK.INI (if present) and set the color to the mode last used. For example, if all data files are on disk drive B: in subdirectory ASTROCLK and you want to force monochrome display, the following command should be used: ASTROCLK B:\ASTROCLK/M ******************** * IMPORTANT NOTE * ******************** Once ASTROCLK has been executed the first time, the drive and path information are saved in the program initialization file ASTROCLK.INI. Thereafter, ASTROCLK uses the information in ASTROCLK.INI and overrides any drive or path specification entered on the command line. However, the command line color options (/M, /R, or /G), if present, will take precedence over ASTROCLK Astronomical Clock and Celestial Tracking Program Page 13 the previous color saved in the file. Use Function Key ALT-F10 to change the drive and/or subdirectory from within ASTROCLK, or delete file ASTROCLK.INI at the DOS prompt to start over. See the section SETTING PROGRAM OPTIONS for additional information. * * * * * Running Program ASTROCLK When ASTROCLK begins, a title screen will appear and the program will perform various initialization tasks. After a few seconds ASTROCLK will display the Local Standard Time (or Daylight Time if it has previously been set using the DAYLIGHT FLAG entry with Function Key ALT-F10) in the main display window and all clocks will be running. For time zones in the United States, the correct zone name will be displayed. The program reads your DOS software clock for the current time and date; set your system clock accurately before you run ASTROCLK using your hardware clock if your computer has one or using the TIME and DATE commands if not. If your version of MS-DOS includes the program RTCLOCK (supplied with some Zenith computers), you may use ALT-F3 to set the system clock from the internal hardware clock. If the program to read your hardware clock has a different name, create a batch file named RTCLOCK.BAT which includes the required command(s), make sure it can be located via the PATH command, and then you may use ALT-F3 to update the software clock. (ALT-F3 may be used to perform any desired task provided it does not disturb the ASTROCLK screen and may be executed as a batch file called RTCLOCK.BAT.) For example, my Zenith Z-151 includes a special (non-Zenith) hardware clock which requires a program called RDCLOCK to set the software clock from the hardware clock. I reset the software clock using the following command in a batch file called RTCLOCK.BAT: RDCLOCK >NUL This reads the hardware clock, sets the software clock, and sends its screen output to the "bit bucket" (throws it away to a special DOS device called "NUL") so that it does not disturb my ASTROCLK display. I have also noticed that for some systems the software clock is not set properly when the system boots but is slow by some five or ten seconds. This may be a peculiarity of the Zenith MS- DOS 3.2x software being used on the system in question, but apparently the computer reads the hardware clock at some point during the boot process, then does something which suspends the clock before it turns the system over to me. I have solved the problem by inserting the RTCLOCK command near the end of my AUTOEXEC.BAT file. Now the software clock is set again after all of the odds and ends have been gotten out of the way. If you do not have a program which reads your hardware clock, or if you do not have a hardware clock, you can exit ASTROCLK temporarily back to DOS using Function Key F9 and set or reset ASTROCLK Astronomical Clock and Celestial Tracking Program Page 14 the time and/or date with the DOS TIME and DATE commands. Then enter EXIT to return to ASTROCLK. It is also possible to "fool" ASTROCLK by setting the DOS system clock to any desired date and time. However, because of an internal DOS software limitation, the DOS clock may only be set for years from 1980 through 2199; in general, I recommend that you use ASTROCLK's SIMULATION mode of operation for non-current dates. ************* * CAUTION * ************* Beginning with DOS Version 3.3, the DOS DATE and TIME commands may set BOTH the software AND the hardware clocks for most 286-class through 486-class computers as well as some others. Therefore, do NOT use the DOS DATE and TIME commands with DOS Version 3.3 and higher if you wish to preserve the setting of the hardware clock. The program automatically presets the celestial coordinates for the star POLARIS (Alpha Ursae Minoris), the first and brightest star of the constellation Ursa Minor, the Little Bear. POLARIS is commonly referred to as the pole star because of its close proximity to the celestial (and geographical) North Pole. As a result, it has long been used for navigation and the alignment of astronomical instruments. More recently, it is often used to align satellite dishes. Since I don't know where you live, the program starts out with the geographical coordinates for Rancho Palos Verdes, California, near Los Angeles. These coordinates are displayed in the lower left portion of the screen. However, in order to use the various time and tracking features for your own location, ASTROCLK needs to know your local longitude (West is negative) and latitude (South is negative). Goode's World Atlas, 17th Edition, (see BIBLIOGRAPHY) is an ideal reference for this purpose; the Index contains some 30,000 cities and other locations worldwide along with their geographical coordinates to a precision of one minute. While I cannot vouch for the accuracy of the data, Goode's is the only atlas I know with this information, a new feature with the 17th Edition. With a little care, your local coordinates can also be interpolated to an accuracy of about ten minutes of arc using a good, detailed road map provided the map includes the fiducial marks for longitude and latitude. Use Function Key F6 to input your local coordinates and local place name; see also the section SETTING LOCAL COORDINATES for a listing of the coordinates of selected cities in the United States and Canada. If your location is near one of the these cities, the coordinates can be read directly from file ASTROCLK.CTY. The file is in standard ASCII code, and may be edited to include additional cities and locations using any editor provided the proper format is observed; WordStar and other word processor users, use the ASCII or "Non-document" mode. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 15 Both geographical and celestial data can be entered (and displayed) in several different formats. Celestial coordinates may be entered or displayed as degrees plus decimal degrees, degrees plus minutes and decimal minutes, or degrees plus minutes plus seconds and decimal seconds. All of these methods are acceptable to ASTROCLK although the separator varies (colon or comma for times, comma for degrees and dates). * * * * * EUROPEAN USERS PLEASE NOTE Both in this documentation and in program ASTROCLK itself, the period (point, ".") is used for the decimal point to separate the integer and fractional parts of a number rather than the comma (virgule, ",") as is the practice in many European countries. This usage is sufficiently deeply buried in the software that it is impractical to make it dynamically configurable. American users have to contend with dates entered in the European style (DD,MM,YYYY), so I've managed to make things a little inconvenient for everyone! Egalement ici dans cette texte et en le programme ASTROCLK, le point (".") plutot que la virgule (",") est utilize pour separer les deux parties d'un nombre, le nombre entier et le fragment. C'est usage commun ici aux Etats Unis. Domage, mais il faut que les Americains utilizent les dats comme les Europeennes (jour, mois, ans). C'est dificile pour tous le monde! [Traduction grace a Dictionnaire Larousse, moins les accents.] * * * * * When ASTROCLK first starts, the current Local Standard Time is displayed in the main window in large numerals. The number keys 0 through 9 (on the top row of the keyboard) and several other keys select the display mode for the main window: 1 LST/LDT Local Standard/Daylight Time 2 UTC Coordinated Universal Time 3 LMST Local Mean Sidereal Time 4 GMST Greenwich Mean Sidereal Time 5 TDT/ET Terrestrial Dynamical/Ephemeris Time 6 Perpetual Calendar 7 Additional Date Information 8 Precision Time and Data Displays 9 Planetary Data Displays 0 Celestial Tracking Display A Alarm Countdown Display [if Alarm is set] N Navigation Display [if Nav Mode enabled] P Planet & Minor Planet Selection T Interval Timer Display Function Key F1 gives quick help for the function keys, but should not be considered a substitute for this documentation. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 16 Function Key F7 may be used to toggle between several display formats for times and angles including whole units (hours or degrees as the case may be) plus decimal units, or a more conventional display (hours, minutes, seconds or degrees, minutes, seconds). This may be useful for comparison with other data in order to utilize the same notation. With the exception of the Julian Date (which is displayed to six decimal places), the running clocks are displayed to the nearest second. Other data are displayed to 0.000001 degrees or hours, 0.0001 minutes of time or arc, or to 0.01 seconds of time or arc, depending upon the display format selected with Function Key F7. The Precision Time Display (Display Mode 8) gives various time information to a precision (and approximate accuracy) of 0.0001 seconds. Most internal calculations are made in QuickBASIC's DOUBLE PRECISION data format to yield maximum accuracy and precision, but not all data are necessarily accurate to the precision displayed. See the section PRECISION AND ACCURACY TESTS for additional discussion. When the clocks are ON, ASTROCLK checks the system time and attempts to begin a new set of calculations each second. Since these calculations tend to be complex and time consuming, some slower computers may not finish the task within the allotted time. My Zenith Z-183 laptop, running at 8 MHz but with no math coprocessor, skips every third or fourth second when operating in the Target Tracking Mode and the Precision Time and Data Displays. This does not affect the accuracy of the displayed data, only the frequency with which it is updated. For comparison, my old Zenith Z-151 running at 4.77 MHz but with an 8087 math coprocessor, manages to keep up just fine. Regardless of the computer type, a math coprocessor will substantially decrease computation times. Version 4.50 of Microsoft's QuickBASIC, the programming language used for ASTROCLK, automatically senses the presence of a math coprocessor and uses it if it is available. To exit ASTROCLK, press ESC and you will return to the DOS prompt. ASTROCLK always rewrites the file ASTROCLK.INI prior to exit in order to reflect the current coordinates, flags, display modes and other information. Each time ASTROCLK is started it checks for file ASTROCLK.INI and reads its contents if present. If you change these data, the new data will be used the next time you run ASTROCLK. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 17 FUNCTION KEYS AND HELP Function Key F1 invokes a HELP function which displays the operation performed by the ten Function Keys, F1 through F10 (as well as several ALT or SHIFT plus Function Key combinations). While the operations are generally self explanatory, positioning the flashing red pointer at the desired operation (F1 through F10) with the Up or Down arrow keys and pressing RETURN will display additional information. Pressing the desired Function Key directly will also display the supplementary information for that Function Key. Press RETURN (or any other key) to return to the main HELP menu. Press the SPACE BAR to exit the main HELP menu and return to normal program operation. All of the displayed clocks are stopped while using HELP and the message "Clocks OFF" will be displayed in flashing red at the upper right of the screen. If the clocks were on when HELP was requested, the clocks will resume normal or simulated operation when you leave HELP and the message "Clocks ON" or "SIMULATION" will again be displayed in green or yellow respectively at the upper right of the screen. If the clocks were off when HELP was requested, they will remain off when you leave HELP. The following operations are available with the ten Function Keys, F1 through F10: F1 Display HELP screens. Display program name, version, and date if pressed again when the main HELP screen is visible. Press SPACE BAR to return to ASTROCLK. F2 Display Target Object EPHEMERIS. Before pressing F2, set the desired start time using F3, then select the desired target object using F5. Press F2 and enter the desired step interval and the number of intervals. The ephemeris information is displayed on the screen. When done or if more than 20 intervals are requested, the display will pause; press any key to contiue. Use the SHIFT-PrtSc to obtain a printed copy of the ephemeris. F3 Set LOCAL/UT TIME and/or LOCAL/UT DATE. The on-screen clocks are running when the time and date are set to the system clock or when the SIMULATION mode has been enabled with ALT-F4. (If the clocks are stopped, press F4 to restart the clocks.) When entering time or date, press RETURN to skip an entry and leave that item unchanged. F3 automatically cancels the SIMULATION mode. LOCAL/UT/TDT TIME: Enter as Hours, Minutes, Seconds using 24 hour notation; use either the comma or the colon as separator. Decimal fractions are permitted for any item. Add the letter "U" at the end of the entry to enter UT TIME instead of local time; add the letter "T" or "E" at the end of the entry to enter TDT/ET TIME instead of local time. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 18 NOTE: Use ALT-F10 to set the DAYLIGHT FLAG and any required ZONE CORRECTION. See the section SETTING PROGRAM OPTIONS for an explanation. LOCAL/UT DATE: Dates may be entered in a number of formats. For "standard" dates, enter the new date in the form DD,MM,YYYY. Note that the date is entered European style: Day, Month, Year and that the full 4- digit year is required. Years B.C. (Julian proleptic calendar) are preceded by a minus sign (e.g. -4713). NOTE: There is no year 0000 in the day numbering algorithms used in ASTROCLK. Add the letter "U" following the year to enter UT DATE instead of local date. When UT TIME has been entered, UT DATE is automatically entered rather than LOCAL DATE. Dates may also be entered as the Julian or Sidereal date. Five styles of day numbers may be used, selected by the prefix used, as well as several other methods. For a more complete explanation of time and date entry using F3, see the section SETTING LOCAL/UT/TDT TIME AND DATE. Use ALT-F3 to read the hardware clock with program RTCLOCK from within ASTROCLK. (See PROGRAM OPERATION for details.) Use SHIFT-F3 to set an ALARM TIME or to set the start time for the INTERVAL TIMER. The alarm may be set up to 23 hours in advance. When set, a window appears at the lower right of the screen and displays the set alarm time and the time remaining in red. To set the start time for the Interval Timer, suffix the entered time with the letter T. To disable an already set alarm, press SHIFT-F3 then press RETURN. See also the section ALARM AND INTERVAL TIMER OPERATIONS for additional information. F4 Toggle Clocks ON or OFF. When clocks are ON, all time and date displays are referenced to the computer's internal software clock and any manually set local time or date is lost. When clocks are OFF, all times on the screen are frozen. The clocks are automatically turned OFF if either the local time or local date is set with Function Key F3. The message "Clocks ON" (green), "Clocks OFF" (flashing red), or "SIMULATION" (yellow) appears at the upper right of the screen to indicate the current clock status. Use ALT-F4 to toggle simulated real time. First preset the desired time and date using Function Key F3, then press ALT-F4 to turn on the simulation. The word SIMULATION will appear in yellow at the upper right of the screen (in place of the Clocks ON/OFF message) when simulation is active. Press ALT-F4 again to disable ASTROCLK Astronomical Clock and Celestial Tracking Program Page 19 simulation. Function Key F3 also cancels the simulation mode. NOTE: Unlike the DOS clock, which may only be set for the period 1980 through 2099, the internal ASTROCLK simulation will operate for any time and date. Function Key F4 may be used to start and stop the clocks in the simulation mode as usual. Function Keys F4 and ALT-F4 stop simulated time in different ways. When F4 is used to stop and start simulation, the simulated time will resume as if the clocks had not been stopped (the same as in the real time mode). Use of ALT-F4 disables the simulation and stops the clocks; pressing ALT-F4 again will restart simulation at the current indicated time. If F4 is pressed after ALT-F4 has stopped simulation, normal real time operation will follow. F5 Set new star or celestial object TARGET COORDINATES using either the internal star database or an external star catalog. [NOTE: To set the target coordinates for a planet or to use the external Minor Planet Catalog, see the sections PLANETARY DATA DISPLAYS and MINOR PLANET SELECTION.] A sub-menu is displayed offering the following function key selections: F1 Enter the USNO Standard Navigational Star Number (1 through 57, or 0 for Polaris) or the desired Star Name to use the internally stored star data. When the name is entered, upper or lower case may be used and only sufficient letters to unambiguously identify the star name are required. Enter "Deneb " (with a trailing space) to distinguish that star from "Denebola". F2 Search for nearest USNO Standard Navigational Star. Enter the local horizon coordinates in degrees: ALTITUDE (the angle from the true horizon up to the star) and AZIMUTH (the direction of the star in the sense North=0, East=90, South=180, and West=270). The program will search for the USNO star closest to the position specified and the data for that star will be displayed in the Tracking Window. F3 Search EXTERNAL STAR CATALOG by star name, star identification, or catalog number. When the name is entered, upper or lower case may be used and only sufficient letters to unambiguously identify the star name are required. (Enter "Deneb ", with a trailing space, to distinguish that star from "Denebola".) Messier objects may be identified by common name ("ORION") or by Messier number ("M9"). If the program finds a matching entry in the ASTROCLK Astronomical Clock and Celestial Tracking Program Page 20 catalog, the data for that star will be displayed in the Tracking Window; if no match can be made, the data in the Tracking Window is left unchanged. Press SPACE BAR to cancel the catalog search in progress; the current data is left unchanged. F4 Search EXTERNAL STAR CATALOG by Right Ascension and Declination. Enter the coordinates when requested and the program will find the catalog stars closest to the position specified. Respond "Y" to display the 10 closest stars or "N" to only locate the closest star. Press RETURN to display the star in the Target Tracking Window. Press SPACE BAR to cancel the catalog search in progress; the current data is left unchanged. F5 Search EXTERNAL STAR CATALOG for nearest star. Enter the local horizon coordinates in degrees: ALTITUDE (the angle from the true horizon up to the star) and AZIMUTH (the position of the star in the sense North=0, East=90, South=180, and West=270). The program will search the catalog for the stars closest to the position specified. Respond "Y" to display the 10 closest stars or "N" to only locate the closest star. Press RETURN to display the star in the Target Tracking Window. Press SPACE BAR to cancel the catalog search in progress; the current data is left unchanged. F6 MANUAL DATA ENTRY. Enter the celestial coordinates, Right Ascension and Declination, the proper motion in Right Ascention and Declination per Julian century (in seconds of time or arc), and the object name as requested. If the proper motion parameters are not known, press RETURN to enter zero. If RETURN is pressed for the object name, the display will show "Manual Target Data". The data for the object will be displayed in the Tracking Window. RETURN Cancel entry of Target Coordinates, leave current Target Coordinates unchanged, and resume normal program operation. When searching using local horizon coordinates, altitude is measured in degrees up from the true horizon; 0 degrees is the horizon and 90 degrees is directly overhead. Don't forget to take into account hills or other obstructions that may obscure the true horizon. Azimuth is measured in degrees from true North in the sense NESW; thus, 0 degrees is North, 90 degrees is East, 180 degrees is South, and 270 degrees is West. The star selection algorithm used in the various searches attempts to pick the Standard Navigational ASTROCLK Astronomical Clock and Celestial Tracking Program Page 21 Star or external catalog star which is closest (angular difference) to the coordinates you have entered. It may take a little practice before you can look at the night sky and estimate star positions accurately enough for the program to select the correct star. While the search is in progress, the message "SEARCHING ..." will appear at the upper right of the screen and the clocks will temporarily be stopped. For an external catalog search, file ASTROCLK.CC1 must be present or another catalog name must have been substituted using ALT-F10, SET PROGRAM OPTIONS. This catalog includes data for 1644 stars, Epoch J2000.0, extracted from USNO STAR1.CAT and USNO MESSIER.CAT. Stars may be requested by catalog number or by any of several names. See the section USING EXTERNAL STAR CATALOGS for additional information. While the search is in progress, the message "SEARCHING ..." will appear at the upper right of the screen and the clocks will temporarily be stopped. NOTE: The supplied external star catalog is a large file, currently about 75Kb, and the search time on a floppy disk system can be slow; the numbers appearing during the search indicate progress through the catalog in increments of 100. For manual data entry, you must know the standard equatorial coordinates, Right Ascension and Declination, for the celestial object you wish to track. Star Atlases, astronomical magazines, and other publications usually give the coordinates for objects of interest. The input routine is very flexible and data may be entered in a number of formats. Observe the separator requirement: items for time (including Right Ascension) must be separated by the colon or comma, while items in degrees (including Declination) must be separated by the comma. In general, only the first item (hours or degrees) is required and a decimal fraction is allowed for all items. If you press RETURN for an item, the data for that item will be left unchanged. When entering data manually, the parameters for proper motion are requested. Press RETURN to enter zero. These data are used by ASTROCLK to calculate the current apparent equatorial coordinates on the Tracking Display and are also used if the coordinates are precessed from one epoch to another using Function Key F8. This information is given for many stars in star catalogs such as SKY CATALOGUE 2000.0. However, note that ASTROCLK requires this information in SECONDS PER JULIAN CENTURY (36525 days) and not all references use the same units; SKY CATALOGUE 2000.0, for example, uses SECONDS PER YEAR which must be converted prior to input into ASTROCLK. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 22 ALT-F5 Because of its usefulness, the coordinates of the star POLARIS (Alpha Ursa Minoris), the pole star, are hard coded into ASTROCLK on Function Key ALT-F5. POLARIS is often used for navigation and for the initial alignment of celestial telescopes and satellite dishes. Press this key and the coordinates for POLARIS are automatically entered and the display mode is switched to the Target Tracking Display. F6 Set new LOCAL COORDINATES. All entries are in degrees and require the comma as separator between the items. A decimal fraction is allowed for any item, and only the first item (degrees) is required. See the section SETTING LOCAL AND DESTINATION COORDINATES for details. If file ASTROCLK.CTY (or an alternate city file) is present, it may be used to read the coordinates for a selection of cities. Enter the name of the location desired in upper or lower case. Only letters sufficient to uniquely identify the location are required. Press RETURN to ACCEPT the displayed location; press SPACE to search for the next match. Press ESC during the search to cancel the search and leave the local coordinates unchanged. If no match can be found, a CAUTION message will be displayed at the lower left of the screen. Press RETURN to continue; the local coordinates will be left unchanged. To enter coordinates manually, press RETURN when prompted for the name. Then enter the LONGITUDE, LATITUDE and ELEVATION, followed by the NAME of the location. NOTE: Additional city files may be available from time to time on my BBS or by mail; see the end of the section A BRIEF EDITORIAL for the BBS telephone number and my address. SHIFT-F6 Set DESTINATION COORDINATES for use with navigation functions. Operates in all respects like F6 above except that the destination coordinates are set rather than the local coordinates, and you may enter "*" instead of a destination name to set the DESTINATION coordinates to the current LOCAL coordinates. ALT-F6 Set LOCAL CONDITIONS for Elevation, Temperature, and Pressure. Allows the user to set these conditions to determine horizon dip and refraction. Automatic con- version between metric and English units is performed. F7 Set DISPLAY FORMAT for the main display window and Local Coordinates window. When the program is started, all angles and times on the main display window (other than ASTROCLK Astronomical Clock and Celestial Tracking Program Page 23 large character times) and in the Local Coordinates window are shown in Degrees/Hours-Minutes-Seconds format. Press F7 to cycle between display formats; the three available formats are: ANGLES TIMES ------------ ----------- DDD MM SS.SS HH:MM:SS.SS DDD MM.MMMM HH:MM.MMMM DDD.DDDDDD HH.HHHHHH Press ALT-F7 to change Target Display coordinates from Right Ascension (hours) to Sidereal Hour Angle (degrees) and from Hour Angle (hours) to Greenwich Hour Angle (degrees), preferred by navigators and given in references such as the Astronomical Almanac. Press ALT- F7 again to return to the original format. Declination is not affected. See also the section TARGET TRACKING DISPLAY for further discussion. F8 PRECESS Internal Star Database. This function allows the user to precess (adjust for different epochs) the current target data and the preset star database in the program. Upon startup, all data are set for epoch J2000.0, the current standard epoch. Press the "Y" key to make the precession calculations or press RETURN to cancel the calculations and leave all data unchanged. If you proceed, press RETURN to restore all data to Epoch J2000.0 or enter the desired new epoch. The new epoch may be entered in any of the following formats: dd,mm,yyyy Calendar Date JDnnnnnnn.nnnnnn Julian Date DJDnnnnnn.nnnnnn Julian Date (J1900.0) MJDnnnnnn.nnnnnn Modified Julian Date Jyyyy.yyy Julian Epoch Byyyy.yyy Besellian Epoch +nnn Add nnn days to Current JD -nnn Subtract nnn days from Cur JD * Current Julian Date and Time # Current Julian Date @ 0h UT Lower case letters (yyyy, nnnnnn, etc.) represent numbers while upper case letters (JD, J, etc.) are used to designate the data format being used. The calendar date method assumes the Julian or Gregorian calendar as determined by the date and the Calendar Flag (See ALT- F10, Setting Program Options). Except for the calendar date method, any number of digits to the right of the decimal point may be input although more than about six will not be significant. Regardless of the data format used for input, the date is internally converted to the corresponding Julian Date for use in the precession calculations. The current ASTROCLK internal database ASTROCLK Astronomical Clock and Celestial Tracking Program Page 24 epoch is always shown in the Target Tracking Display, Display Mode 0, and in the initial Precession instructions when using Function Key F8. Care should be taken when manually entering data whose epoch is different from that of the internal database. In order to maintain consistent data within ASTROCLK, the internal star database should first be precessed to a data epoch, then manual data referenced to that epoch should be entered. After that, all data may be precessed to the final epoch; using this procedure, both the manually entered data as well as the internal data will always refer to the same epoch. For example, to track a target using Epoch J2000.0 coordinates when the available catalog data is for Epoch B1950.0, first precess the internal star data to B1950.0 using F8, next enter the target Right Ascension, Declination, Name from the catalog, and the proper motion in Right Ascension and Declination (if known) using F5 (and F6 for manual entry). Finally, again use F8 to precess all data back to Epoch J2000.0 (or any desired epoch). Thereafter, F8 may be used as many times as desired to precess the database. F9 DOS SHELL. This function invokes a copy of the MS-DOS executive, COMMAND.COM, and allows the user to enter any legal DOS command. COMMAND.COM must be available or ASTROCLK will ignore the request and continue normal operation. Since COMMAND.COM must reside in available memory in addition to ASTROCLK, use of a large RAM DISK or TSR program may cause the DOS shell to fail. The MS- DOS prompt is displayed and the computer performs in most respects exactly as usual. However, far less memory is available and therefore programs which require very large amounts of memory for their execution may not operate properly with the SHELL. Enter EXIT to return to ASTROCLK and resume operation with all data and parameters unchanged. SHIFT-F9 may be used to automatically executa a preset DOS command or batch file. The DOS command is set using ALT-F10, SETTING PROGRAM OPTIONS, and is saved in file ASTROCLK.INI. If a DOS command has been set, the command is executed and upon completion ASTROCLK is automatically resumed. This command has the same restrictions and comments as the normal F9 command above; the only difference is the execution of a preset DOS command and automatic return to ASTROCLK. The default is no action. ALT-F9 may be used to automatically execute the USNO Interactive Computer Ephemeris (ICE) or the USNO Floppy Almanac (FA); see the section USNO EPHEMERIS PROGRAMS ASTROCLK Astronomical Clock and Celestial Tracking Program Page 25 for more complete information. ALT-F9 will execute the selected USNO program if the appropriate software has been installed in the computer AND if the appropriate ephemeris has been selected and its path set using ALT- F10, SETTING PROGRAM OPTIONS. F10 Function Key F10 provides navigational calculations using two methods: DEAD RECKONING and SIGHT REDUCTION. For an observer in motion, ASTROCLK also calculates the current position based upon the last "fix" and the observer's course and speed. See the section CELESTIAL NAVIGATION for details. ALT-F10 is used to set or change various ASTROCLK program options. See the following section, SETTING PROGRAM OPTIONS, for details. 0-9 Select Display Window Mode. The system starts out with LOCAL STANDARD/DAYLIGHT TIME displayed in large characters. In the United States, the correct time zone name (i.e. "PACIFIC") replaces the word "LOCAL". Press the number key associated with each display mode to change to that mode. (Use the numbers at the top of the keyboard rather than the number keys on the keypad at the right unless NUMLOCK is ON.) The available numeric modes and alphabetic commands are: 1 Local Standard or Daylight Time (LST/LDT) 2 Coordinated Universal Time (UTC) 3 Local Mean Sidereal Time (LMST) 4 Greenwich Mean Sidereal Time (GMST) 5 Local Mean Solar Time 6 Perpetual Calendar and Holidays 7 Julian Date Information 8 Precision Time Display 9 Planetary Data 0 Target Tracking Display N Select NAVIGATION Display Mode P Select PLANET or MINOR PLANET (forces display mode 9 or 0) A Alarm Countdown * S Start/Stop Interval Timer * T Interval Timer * Z Stop and Reset Interval Timer * * See the section ALARM AND INTERVAL TIMER OPERATIONS for information on these modes. While in display mode 0, Target Tracking, use the UP and DOWN arrow keys to select the next or the previous Standard Navigational Star. PgUp and PgDn increase or decrease the selected star number by 10. Use F5 to ASTROCLK Astronomical Clock and Celestial Tracking Program Page 26 input a new star number directly. While in display modes 1 through 5, the large clock displays, use the UP and DOWN arrow keys to select the dual-time displays and the HOME key to return to single-time display. See the section DUAL-TIME DISPLAYS for further information. While in display mode 6, Perpetual Calendar, press "6" to toggle between calendar display and list of holi- days, and use the Left and Right arrow keys to change months, the Up and Down arrow keys to change years, and the PgUp and PgDn keys to change the years by decades. HOME returns the display to the current system date. Use F3 to input a new date or time directly. While in display mode 8, Precision Time and Data Displays, press PgUp or PgDn to view the next Precision Time or Data Display. See the section PRECISION TIME AND DATA DISPLAYS for details. While in display mode 9, Planetary Data, use the UP and DOWN arrow keys to change planets. See the section PLANETARY DATA DISPLAYS for further discussion. Pressing "N" to select the Navigation Mode Display will result in an error message if navigation has not been enabled with Function Key F10. See the section NAVIGATION for further discussion. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 27 SETTING PROGRAM OPTIONS Several ASTROCLK program options can be set using Function Key ALT-F10. The options which can be set are shown below. All of this information is saved in file ASTROCLK.INI. The DAYLIGHT FLAG determines whether or not Daylight Time is in effect. The ZONE CORRECTION allows the user to adjust the local time zone. The CALENDAR FLAG determines which of three calendar conventions to use; it is initially set to the Gregorian Calendar (from October, 1582). A sub-menu is displayed when using ALT-F10 with the current values shown enclosed by square brackets, "[...]". Press the function key corresponding to the option you wish to change or press RETURN to resume normal program operation with the options as shown. A typical display showing the default values for each item is shown below: F1 DAYLIGHT FLAG: [OFF] F2 ZONE CORRECTION: [0.00] F3 COLOR FLAG: [ON] F4 ICE/FA FLAG: [0=ICE/FA Disabled] F5 CALENDAR FLAG: [1=Gregorian @ 1582] F6 SET FILE NAMES & PATHS F9 SET DOS COMMAND for use with SHIFT-F9 (no command has been entered) RETURN Resume program operation When you exit ASTROCLK, these options will be saved in file ASTROCLK.INI and will automatically be restored the next time you run the program. Setting the DAYLIGHT FLAG ------------------------- The DAYLIGHT FLAG selects whether or not an additional hour will be automatically added during the time zone calculation to determine Coordinated Universal Time. The flag applies equally to all time zones and the window label for local time will include the word STANDARD if the flag is OFF, or the word DAYLIGHT if the flag is ON. For example: PACIFIC STANDARD TIME or PACIFIC DAY- LIGHT TIME. If you wish to change the state of the flag, press Function Key F1 until the desired mode appears. There are three possible settings: [OFF] DAYLIGHT FLAG always OFF. [ON] DAYLIGHT FLAG always ON. [AUTO ON] or [AUTO OFF] DAYLIGHT FLAG set according to DOS time and date. The DAYLIGHT flag is OFF by default. The UT TIME ZONE OFF- SET, if enabled with F10+F10, will also be automatically adjusted when the DAYLIGHT FLAG is changed. Because the dates for switch- ing to and from daylight (summer) time are different in different ASTROCLK Astronomical Clock and Celestial Tracking Program Page 28 countries and are sometimes changed for one reason or another, use the manual ON or OFF settings for those locations. When the state of the DAYLIGHT FLAG is changed, either manually or as a result of setting the flag to the AUTO mode, the following message will appear: You have changed the status of the DAYLIGHT FLAG. Do you wish the DOS computer clock to be automatically adjusted (Y/n): NOTE: For DOS 3.3 and higher, the hardware clock may also be changed! Press ENTER to automatically adjust the DOS time and date according to the change just made. Press "N" plus ENTER to leave the DOS time and date unchanged. Note that for DOS versions 3.3 and higher AND for 80286 processors and higher, both the software and the hardware clocks will be set; for 8088 processors (XT- class computers), the hardware clock usually is not changed (depending upon the type of hardware clock installed). By selecting the AUTO mode for the DAYLIGHT FLAG, ASTROCLK will automatically select the state of the flag as a function of the DOS time and date. Daylight time is ENABLED as of 02:00 Local Standard Time on the first Sunday in April and is DISABLED as of 02:00 Local Daylight Time on the last Sunday in October. These dates are generally valid ONLY in the United States and Canada. (These dates were effective in the United States beginning in 1988; they were changed periodically prior to that year.) If the DAYLIGHT FLAG is incorrectly set, all calculated times and positions will also be incorrect. Do NOT use the DAY- LIGHT FLAG to adjust for an incorrect zone calculation; use the ZONE CORRECTION (see the following item) for that purpose. You may, if you prefer, leave your computer clock always set to local STANDARD time and the DAYLIGHT FLAG always off. However, you may NOT set your computer clock to UTC (unless you are in that time zone); set the computer clock correctly and use display mode 2 to view UTC instead. Setting the ZONE CORRECTION --------------------------- The ZONE CORRECTION is DISABLED when the Navigation Mode is active. The ALT-F10 menu will show "[disabled]" when this is the case. This is to ensure that standard time zones are calculated correctly during navigation. An attempt to enter a ZONE CORRECTION while the Navigation Mode is active will be ignored. The ZONE CORRECTION allows the user to make special adjustments in the calculation of Coordinated Universal Time (UTC) relative to Local Time. Some time zones are not an integral number of hours offset from UTC; in other cases the actual standard time for a particular location is different from that calculated by ASTROCLK because of the irregular way time zones have been defined locally. Some countries use "Double Summer ASTROCLK Astronomical Clock and Celestial Tracking Program Page 29 Time" which is two hours ahead of the standard time for the zone. To change the current ZONE CORRECTION, press F2. The correction must be entered in hours and decimal fraction, H.HH or -H.HH, and is automatically rounded to the nearest 0.25 hours (15 minutes); the maximum correction is restricted to the range -2.00 hours to +2.00 hours. The ZONE CORRECTION is calculated in ADDITION to the DAYLIGHT FLAG. IMPORTANT NOTE: Unlike the Daylight Flag, which remains unchanged when you change local coordinates, the Zone Correction will be reset to 0.00 hours any time you change the local coordinates on the assumption that the Zone Correction is unique to a given location. This also assures that when using the external city file to change cities and load the coordinates from the file, the Zone Correction will be reset. The default value for the Zone Correction is 0.00 hours. Setting the COLOR FLAG ---------------------- The COLOR FLAG allows you to switch between color, red, green, and monochrome display. COLOR FLAG ON uses various colors for the display. COLOR FLAG RED sets all screen colors to red in order to protect night vision if the computer is operated in a darkened area. GREEN FLAG GREEN sets all screen colors to green; this may help reduce eye fatigue during extended use. COLOR FLAG OFF (monochrome) is used for true monochrome monitors and may be used if you wish a white display on color monitors. Switching to any of the color modes on some true monochrome systems may cause an error. See also the section PROGRAM OPERATION for additional information on the command line color options. To change the COLOR FLAG from one mode to the next, press Function Key F3; the color changes for the new mode will take effect immediately within the window but the balance of the display will not be affected until you leave the Setting Programs Options window by pressing the RETURN key. The state of the COLOR FLAG is saved in file ASTROCLK.INI and the program will use the color mode read from that file the next time it is run. However, the command line color option (/M, /R, or /G), if present, will override the saved state of the COLOR FLAG. Setting the ICE/FA FLAG ----------------------- The ICE/FA FLAG allows you to select between the following three options for external USNO ephemeris programs: 0 = No external USNO ephemeris program is available. Pressing ALT-F9 will display an error message. (DEFAULT) 1 = The USNO Interactive Computer Ephemeris, ICE, is installed and will be executed by pressing ALT-F9. Be sure to set the ICE drive and/or path correctly! ASTROCLK Astronomical Clock and Celestial Tracking Program Page 30 2 = The USNO Floppy Almanac, FA, is installed and will be executed by pressing ALT-F9. Be sure to set the FA drive and/or path correctly! Press F4 until the desired option is displayed. Do not select one of the USNO ephemeris program options unless the appropriate ephemeris files have been installed. Use F6 (below) to set the correct drive and path for ICE or FA. See also the section USNO EPHEMERIS PROGRAMS for additional information. Setting the CALENDAR FLAG ------------------------- The CALENDAR FLAG allows you to select between the following three calendar conventions: 0 = Strict Julian Calandar for ALL dates. Technically, this calendar is known as the Julian Proleptic Calendar for dates prior to 46 B.C. NOTE: The Julian Calendar may not be used in real time (see below). 1 = Julian Calendar switching to Gregorian Calendar in October, 1582 in accordance with standard astronomical convention (DEFAULT). 2 = Julian Calendar switching to Gregorian Calendar in September, 1752 corresponding to usage in Great Britain and her colonies (including the United States). Press F5 to change the flag until the desired calendar convention is displayed. For additional information on the various calendar conventions, see the section DATES AND THE GREGORIAN CALENDAR. NOTE: Regardless of the calendar convention in effect, ASTROCLK always assumes that the system clock is set to the correct date. This means that only calendar flag values of 1 and 2 are permitted with the CLOCKS ON. ASTROCLK's internal date functions are performed using the current Julian Date. Therefore, switching from the Gregorian Calendar to the Julian Calendar for a modern date with the CLOCKS OFF will leave the Julian Date unchanged but will change the calendar date to a new value, correct for the strict Julian Calendar. However, if the clocks were ON, they will automatically be set to OFF and a warning message will be displayed. If you wish to use the program with the Julian Calendar and the clocks running, use the SIMULATION mode (ALT-F4). Setting the FILE NAMES and PATHS -------------------------------- In order to execute the help function, to utilize the external data files and to run the USNO Interactive Computer Ephemeris (ICE) or Floppy Almanac (FA), ASTROCLK must know what the file names are and where to find them. The default condition is that these files are all located in the current directory and ASTROCLK Astronomical Clock and Celestial Tracking Program Page 31 that the files have the following names: ASTROHLP.EXE External Help Program ASTROCLK.CC1 External star catalog ASTROCLK.MPC External minor planet catalog ASTROCLK.CTY External city file ICE.EXE USNO Interactive Computer Ephemeris FAnn.EXE USNO Floppy Almanac (nn=88-99) There is a different file for each year for the USNO Floppy Almanac. All files required by ICE or FA must be located in the same directory as the corresponding .EXE file. A common drive and path may be specified in the command line when starting ASTROCLK for the first time. ******************** * IMPORTANT NOTE * ******************** Once ASTROCLK has been executed the first time, the drive and path information are saved in the program initialization file ASTROCLK.INI. Thereafter, ASTROCLK uses the information in ASTROCLK.INI and overrides any drive or path specification entered on the command line. You may use ALT-F10 and then F6 to change the drive and/or subdirectory from within ASTROCLK, or you may delete file ASTROCLK.INI at the DOS prompt to start over. * * * * * Since the external city file, ASTROCLK.CTY, is a conventional ASCII file which may be created or edited by the user, and since alternative external star catalogs are or may be available, a provision is included here to permit the user to specify an alternate file name for either of these files, including drive and path. For example, you might wish to use a special city file when traveling in Europe. The current STAR CATALOG, MINOR PLANET CATALOG, and CITY FILE names are shown on the menu, in that order. If a drive and/or path was specified with the command line, they will also be shown. If no drive or path is shown, ASTROCLK assumes the current drive and directory. To change one or more file names, press F6 and enter the new name when prompted or press RETURN to leave a name unchanged. You may include a drive and path specification if desired. Enter SPACE to restore the file name to the default. (A long path specification may exceed the width of the display window but it will be processed correctly.) For convenience, an additional file, MESSIER.CC1, is available with the data for the 108 Messier objects only. The same data is included in file ASTROCLK.CC1 but at the end of that long file. If you are content with the 57 internal USNO stars plus Polaris and just wish to add the Messier objects, use MESSIER.CC1 and substitute it for ASTROCLK.CC1 using ALT-F10 and then F6. This will substantially reduce the catalog search time, especially on floppy disk based systems. M40 has always been missing and no entry for that object is included; therefore, the ASTROCLK Astronomical Clock and Celestial Tracking Program Page 32 catalog number, indicating the record number within the file, will be one less than the Messier number for Messier objects numbered 41 and above. An alternate city file, USCITIES.CTY is available which includes some 718 U.S. cities with the geographical coordinates given to a higher accuracy than the standard ASTROCLK.CTY. Other special city files and star catalogs may also be available from time to time on my Bulletin Board System (BBS). See the section A BRIEF EDITORIAL near the end of this document for information on the BBS. THE "EASY" METHOD OF SETTING PATHS: If you do not understand paths and subdirectories or simply do not wish to alter ASTROCLK's default setup, simply make sure that all ASTROCLK files (and the USNO ICE or FA files, if you have them) are located on the same drive and directory. I recommend that the files be located on the selected drive in directory ASTROCLK; see your DOS manual for information on how to create the directory and copy the ASTROCLK files to that directory. Then run ASTROCLK from the ASTROCLK directory using the following command (which assumes drive C:): ASTROCLK C:\ASTROCLK All drive and path information will be saved in file ASTROCLK.INI for subsequent uses of the program. Then, if you execute ASTROCLK from the ASTROCLK directory, the program will be able to find all its required files. However, it is often necessary or convenient to have some files, especially the USNO ephemeris files, located in another drive and/or subdirectory. This is particularly true for floppy disk based systems where the individual disk capacity may prevent all files from being on the same disk. The drive and path for ASTROCLK and for the USNO Interactive Computer Ephemeris (ICE) or Floppy Almanac (FA) may be separately set using F6, and specific file names (including drive and directory if desired) may be set for the external star catalog, minor planet catalog, and city files. When setting the ASTROCLK and ICE or FA paths, ONLY THE DRIVE AND PATH ARE SPECIFIED. A backslash ("\") should be the first character of each path except for a blank path; a CAUTION warning message will be displayed if you do not include it. Do NOT add a backslash at the end of the path. Unless you include a drive specification such as "D:", ASTROCLK assumes that all files are located on the current drive. If you include a drive specification with the ICE or FA path, you must also include a drive specification with the ASTROCLK path; a CAUTION warning message will be displayed if you do not include it. Thus, if your ICE/FA and related files are in drive D: and path \FA, enter "D:\FA", followed by RETURN, for the ICE/FA path. Setting the ICE/FA path not only enables ASTROCLK to locate the ICE.EXE or FAnn.EXE files, it also tells ASTROCLK where to write the file ICE.DFT or FA.DFT (which determines the default conditions for the program). ASTROCLK Astronomical Clock and Celestial Tracking Program Page 33 The external file names default to ASTROCLK.CC1, ASTROCLK.MPC and ASTROCLK.CTY, and ASTROCLK also assumes by default that they are all located in the ASTROCLK path. Enter an alternate file name for one or more files if desired. You may include the drive and/or subdirectory if they are different from ASTROCLK's values. Enter a SPACE to reset the file name to the default name. Setting the PRESET DOS COMMAND ------------------------------ This feature, requested by several users, allows you to enter a preset DOS command which will be executed from ASTROCLK each time you press SHIFT-F9. The current preset DOS command is shown on the screen; if no command has been entered or read from file ASTROCLK.INI, the following message will appear: (no command has been entered) Press F9 to select this option and then enter the desired command or the name of the batch file (without the .BAT portion of the file name) which you wish to be executed. Press RETURN by itself to clear the preset DOS command. NOTE: If you select this option by mistake, you must re-enter the desired DOS command or it will be cleared. Once the desired DOS command has been entered, return to ASTROCLK and test the command by pressing SHIFT-F9. Bear in mind that very large programs may require more memory than is available under the SHELL used by ASTROCLK to execute DOS programs. Further, using TSR (Terminate and Stay Resident) programs may leave insufficient memory to use this feature or may cause programs to operate unpredictably. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 34 SETTING LOCAL/UT/TDT TIME AND DATE ASTROCLK has three basic modes of operation: real time, simulated real time, and static. In the real time mode, the clocks are running synchronized to the system clock and the data displayed are calculated every second (computer calculation time permitting). The simulation mode is the same as real time except that ASTROCLK uses a time previously set with Function Key F3 as its reference. Using a Zenith Z-183 laptop computer not equipped with a coprocessor, ASTROCLK is able to make most calculations (except for Tracking and Precision data) within one second. Compared to a Zenith Z-248 8 MHz AT-compatible computer with a math coprocessor, the computational delays are noticeable. Provided the local time, date and coordinates have been properly set, the data reflect the correct real time (or simulated real time) parameters. In the static mode, the data are held at the values for the specified time. Except in the Navigation Mode, an algorithm is used to automatically calculate the time offset from UTC, Coordinated Universal Time based upon the longitude of the local coordinates. UTC is roughly equal to Greenwich Mean Time (GMT) for years 1925 and later. The results of this calculation are shown as UTC ZONE (for example, -118 degrees yields UTC -8.0 for Pacific Standard Time in Southern California), and are used in all subsequent time and position calculations. All calculations are based upon Standard Time. If Daylight Time is in use AND your computer clock is set to Daylight Time, use Function Key ALT-F10, SETTING PROGRAM OPTIONS, and set the DAYLIGHT FLAG ON to automatically adjust the times. To return to Standard Time, set the DAYLIGHT FLAG OFF. ASTROCLK does not perform any date tests to verify the validity of the DAYLIGHT FLAG setting. Because of the strange ways time zones have been drawn, the automatic time zone calculation may not always produce the desired result. The calculated time IS the correct time based upon the division of the world into 24 equal time zones. However, for political reasons or for local convenience, time zones often do not excatly follow the designated meridians. If a location is more than 7-1/2 degrees East or West of the 15 degree meridian corresponding to the local standard time, the time calculations will be an hour in error. Use the ZONE CORRECTION with ALT-F10, SETTING PROGRAM OPTIONS, to correct for this problem to the nearest fifteen minutes. Some time zones are not set at an integral number of hours offset from UTC, fortunately none of them in the United States. A correction of from -2.00 hours to +2.00 hours will be accepted in order to accommodate both time zone errors and double daylight times. For U.S. locations not requiring this special correction, ASTROCLK will automatically display the correct zone name, Eastern, Pacific, etc. In the Navigation Mode, the calculation of times is handled slightly differently. Because the computer may move from one time zone to another, the Navigation Mode requires that the UT TIME ZONE OFFSET, the difference between the computer's clock and Universal Time (UT), be entered using Function Key F10. ASTROCLK then automatically converts the computer clock to UT before ASTROCLK Astronomical Clock and Celestial Tracking Program Page 35 making adjustments for the current longitude (whether calculated or manually entered). This permits the computer to move freely from time zone to time zone without resetting the computer's internal clock. However, there is as usual no free lunch; because the local time is strictly dependent upon the current longitude, no ZONE CORRECTION for time zones which do not correspond to the calculated time is permitted. Any ZONE CORRECTION in effect when the UT OFFSET is set will be cleared. On the other side of the coin, once the UT OFFSET has been set ASTROCLK's local coordinates may be set as desired and the current correct local time will be calculated and displayed and UT TIME will remain constant. ASTROCLK will adjust ALL local times by one hour if the DAYLIGHT FLAG is set; given that the dates when daylight time is in effect vary considerably around the world, users may find it more convenient to leave the DAYLIGHT FLAG off when away from their "home" time zone(s), turning it on only when certain of the local standard. See also the discussion of the UT TIME ZONE OFFSET in the NAVIGATION section. When used in the static mode, the clocks are stopped. The user may enter any desired location or time/date and all calculations will be made using that data. Note that West longitudes and South latitudes must be entered as negative numbers for ASTROCLK. (CAUTION: Some texts and institutions do not observe the same sign conventions!) The basic calculations in ASTROCLK are based upon formulae accurate for Epoch J2000.0. Negative dates, that is dates "B.C.", display in RED (BLINK in all monochrome modes) and there is no year 0000; the sequence of years near zero is -2, -1, 1, 2, etc. The accuracy of some of the celestial data will decrease as the time difference from Epoch J2000.0 increases. Although UTC and UT (=UT1) are not the same, they are maintained to within 0.9 seconds of each other by the occasional insertion of Leap Seconds at the end of June or December. In 1988 the difference is typically less than 0.2 seconds. While software programs are available to precisely set a computer's clock using telephone signals from NBS, this accuracy cannot usually be maintained for extended periods of time. In any event, frequent calls to NBS are impractical for most of us by reason of cost. A more cost effective solution is to use the Heath/Zenith GC-1000 Most Accurate Clock and its optional software to synchronize the computer's clock. The GC-1000 is a combination receiver and clock and when equipped with an RS-232 interface and external antenna, it can maintain UTC time to within 10 milliseconds. I have therefore elected to treat UTC as equal to UT for time and date displays and have actually assumed UT time and date in all but one case: the correct UTC time relative to UT is calculated and displayed on Precision Time Display #1 but it is otherwise not used. All other times and dates are referenced to UT rather than to UTC. This minor technical error represents a compromise between technical accuracy and ease of use. While the times displayed by ASTROCLK in the various small windows are rounded to the nearest second, any time (Local, UT, or TDT) may be entered using Function Key F3 to a precision of approximately 0.0001 seconds and will be used to that precision in the various calculations. Compare the times shown in the small ASTROCLK Astronomical Clock and Celestial Tracking Program Page 36 windows with those in the Precision Time Display #1. Except for some items in the Precision Time Displays, this additional precision is usually not significant. See the section PRECISION AND ACCURACY TESTS for additional comments. Setting the LOCAL/UT/TDT Time The time entry format is very flexible and for convenience will accept either the traditional colon (":") or the comma (",") as the separator between hours and minutes or minutes and seconds; the examples are shown with the colon only. Each item (hours, minutes, or seconds) can accept a decimal fraction although normally only the last item entered would have a fractional part. Time entries are ALWAYS made using the 24-hour convention. The following are all acceptable time entries: HH Hours HH.HHHHHH Hours + fractional hours HH:MM Hours:Minutes HH:MM.MMMM Hours:Minutes + frac mins HH:MM:SS Hours:Minutes:Seconds HH:MM:SS.SS Hours:Minutes:Seconds + frac The "standard" date input format requires the day, month, and year (in that order, European style, and separated by commas) in either of the following two formats: DD,MM,YYYY DD.DDD,MM,YYYY The first format specifies the date to be used with the existing or just input time; unless the letter "U" or "T" has been appended to the time input (see below), the date is the LOCAL date. The second format, containing a fractional day (including "." alone or ".0") specifies a UT date with the time implicit to allow the astronomical convention where dates are often given in the form "1988 JAN 1.5"; this would be entered as "1.5,1,1988". The time input is ignored with this format (press RETURN). The fractional part may have as many digits as desired, but more than about six digits usually are not significant. It is sometimes convenient to set the time and date using UT (=UT1) data. This avoids having to make the conversions mentally. If you add the letter "U" at the end of the time or date entry, ASTROCLK will perform the appropriate time or date conversions automatically, based upon the current settings of the DAYLIGHT FLAG and ZONE CORRECTION. If you add "U" to your time input to enter UT time, ASTROCLK assumes that you are also entering UT date. If you enter a fractional part of a day as part of the date input, the time input is ignored and UT date is assumed (see the preceeding paragraph). As an example, to set the time and date to 9:44:30 UT on November 13, 1978, use the following entries: 9:44:30U (UT time) ASTROCLK Astronomical Clock and Celestial Tracking Program Page 37 13,11,1978 (UT date) Alternatively, the same time and date may be input by pressing RETURN for the time, and using the following date entry (with the fractional part of the day representing the desired time): 13.405903,11,1978 (UT date, time implicit) If Terrestrial Dynamical Time (or Ephemeris Time prior to 1984) is desired, add the letter "T" (or "E") at the end of the time entry. ASTROCLK automatically selects TDT or ET based upon the date regardless of the letter used to designate the time during input. Note that the displayed UTC DATE may not correspond to that input if the time is within the period Delta T (TDT-UT) of midnight. ASTROCLK automatically adjusts the date to agree with the information input and near midnight UTC this can be confusing to the user! Setting the LOCAL/UT Date The date may be input in a variety of formats to suit the circumstances. The "conventional" format is: DD/MM/YYYY Standard Date Format DD,MM,YYYY Standard Date Format Note the DAY, MONTH, YEAR sequence and that the full four digit year is required. Either the forward slash ("/") or comma (",") may be used as the separator. Note also that leading zeros are not required for any part of the date; for example, January may be entered as either "1" or "01". Because astronomical convention and tabular data often employ the 0th of January and the 32nd of December, these exceptions to legal days are permitted. The date input will be interpreted as the local date if local time has been input, or will be interpreted at UT or TDT/ET date if that time format has been used. The date input routine will also permit the entry of the Julian Date (JD), Dublin Julian Date (DJD), Modified Julian Date (MJD), Truncated Julian Date (TJD), or Greenwich Sidereal Date (GSD) by prefixing the date with the appropriate two or three letters followed by the desired date. Whenever letters are used, they may be input in upper or lower case. Note that when an integer GSD is entered (no fraction to the right of the decimal point), the resulting UT time is the Greenwich Transit of the Mean Equinox at 0h GMST for that date. The following formats are available: JDddddddd.dddddd Julian Date DJDddddddd.dddddd Dublin Julian Date MJDddddddd.dddddd Modified Julian Date TJDddddddd.dddddd Truncated Julian Date GSDddddddd.dddddd Greenwich Sidereal Date Decimal fractions of a day may also be included, as shown ASTROCLK Astronomical Clock and Celestial Tracking Program Page 38 above and in the subsequent examples, but more than six digits to the right of the decimal point will probably not be significant in most calculations. If the current date plus or minus a number of days is desired, the form +nnn or -nnn may be used with "nnn" being the desired number of days. Entering "#" alone will yield the current Julian Date at 00:00:00 UT; entering "*" alone will yield the exact current Julian Date (useful for precession calculations with Function Key F8). Examples: +3 Current JD + 3 days -10 Current JD - 10 days +1.5 Current JD + 1.5 days # Current JD @ 00:00:00 UT * Current JD Similarly, dates may be input as Julian or Besselian Epochs by prefixing the epoch with the letter "J" or "B" respectively. Two formats are available: Jyyyy.yyyyyy Julian Epoch Byyyy.yyyyyy Besselian Epoch Finally, inspired by the desire to interpret dates on images during Voyager 2's close encounter with Neptune in August 1989, dates may be input as the current Day-of-the-Year, with January 1 being Day 1. Note that this method may ONLY be used for the year currently set and displayed. UT Hours, minutes and seconds may be included if desired, as shown by the following format examples: Dnnn[.nnnn] Day Number Dnnn:hh[.hhhh] Day + UT Hours Dnnn:hh:mm[.mm] Day + UT Hours+Minutes Dnnn:hh:mm:ss[.ss] Day + UT Hrs+Mins+Secs When these special forms of date input are used, you may press RETURN in response to the time prompt since UT time is implicit in the date format; any time that is input will be overridden and the implicit time associated with the date used instead. All of these date formats are calculated in Display Mode 7, Julian Date Information, and that display may be used to easily convert dates from one format to another; while in Display Mode 7, use F3 to enter the date in one format and read the desired conversion on the screen. For example, the following date entries are equivalent to July 2, 1988 at 03:00:00 UT to within a few seconds: JD2447344.625 DJD32324.625 MJD47344.125 TJD7344.125 GSD2454045.903811 D185.125 (current year must already be 1988) J1988.5 ASTROCLK Astronomical Clock and Celestial Tracking Program Page 39 B1988.501032 NOTE: If you enter a date as a simple number, greater than 400 and without a letter or sign prefix such as "JD" or "+", ASTROCLK assumes that you wish to enter the Julian Date and simply neglected to include the "JD" prefix. The program therefore interprets such entries (up to the first comma, if present) as Julian Dates and no warning or error message is generated. (ASTROCLK versions prior to 8831 would sometimes generate a QuickBASIC error and abort ASTROCLK in this situation because the number was interpreted as the day of the month.) Setting the time/date from NIST/USNO When precision and accuracy are required, the computer clock may be set remotely using the telephone time service of either the National Institute of Standards and Technology (NIST, formerly the National Bureau of Standards or NBS) or the U.S. Naval Observatory (USNO). This method is available for systems using DOS version 3.3 or higher AND equipped with 80286 processor or higher; some 8088-equipped systems may also use this method depending upon the type of clock hardware installed and the version of DOS being used. The recommended method uss the program TIMESET; the current version of TIMESET is posted on my bulletin board system. TIMESET is a copyrighted program by Peter Petrakis which is distributed using the "shareware" concept. If not available on a convenient bulletin board system, TIMESET may be obtained by writing: Life Sciences Software 8925 271st N.W., Suite 112 P.O. Box 1560 Stanwood, WA 98292 (206) 387-9788 US$35.00/copy (as of April, 1991) TIMESET is an elegant and very precise method for setting the hardware and software clocks in your computer. You must have a modem connected to your system to use TIMESET. Note that the process involves making a telephone call to either Boulder, CO or Washington, DC and toll or long distance charges may apply! Although TIMESET can set your computer clocks to an accuracy of within 2 milliseconds under the best conditions, this only yields short term accuracy. It is important to remember that since the computer's hardware clock "ticks" occur at 55 millisecond intervals and hardware clocks drift at varying rates depending upon the particular hardware, long term accuracy and precision can only be achieved by regular calibration and long term drift measurements. The frequency with which you use TIMESET is a function of your accuracy requirements. Further information is given in the TIMESET documentation. ASTROCLK may easily be set up to use TIMESET on demand by ASTROCLK Astronomical Clock and Celestial Tracking Program Page 40 using ALT-F10 to enter the preset command. With TIMESET in the same directory as ASTROCLK, the preset command is: C:\ASTROCLK\TIMESET Substitute the drive and directory appropriate to your system or be sure TIMESET is available via your DOS PATH. TIMESET may then be executed at any time by pressing SHIFT-F9. The time and date will be set (if the NIST or NBS telephone number is not busy) and then ASTROCLK will automatically resume operation. One potential source of error or confusion is daylight savings time. TIMESET must be manually set to handle these time changes so as to agree with the current setting of the DAYLIGHT FLAG in ASTROCLK. NOTE: Don't forget to configure TIMESET as described in the documentation. Be sure to set the program for automatic operation so that it will return to ASTROCLK when it has completed setting the time and date. TIMESET may also be used directly from the DOS prompt. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 41 SETTING LOCAL AND DESTINATION COORDINATES Before most of the data displayed by ASTROCLK can be of any practical use, you must set your own geographical coordinates into the program using Function Key F6. On startup, ASTROCLK uses the coordinates for Rancho Palos Verdes, California, near Los Angeles. If you do not know your coordinates, I recommend that you consult Goode's World Atlas, 17th Edition, which includes an extensive Index with longitudes and latitudes of some 30,000 cities and other locations worldwide. All coordinates are given to one minute of arc, and this is the only atlas I know which includes this information. NOTE: In spite of the format used for the coordinates in Goode's, 118.34 for example, the portion to the right of the decimal point represents minutes NOT decimal parts of a degree. See the BIBLIOGRAPHY for the full reference. With the addition of navigation functions to ASTROCLK, Function Key SHIFT-F6 has been included to allow destination data to also be read from the same "city file". The operation of SHIFT-F6 is identical to normal operation of Function Key F6 decribed below except that the DESTINATION name and geographic coordinates are set rather than the LOCAL name and coordinates. The destination data are disabled when ASTROCLK is first started. See the section CELESTIAL NAVIGATION for additional discussion. The following prompt will appear in the main window after pressing F6: SET LOCAL COORDINATES Enter CITY NAME to search for in file C:\ASTROCLK\ASTROCLK.CTY Enter desired name: _ Match starts at left of name. Prefix input with '/' to match input anywhere within the name. Matches are case insensitive. Press RETURN for MANUAL data entry. The current values for the LOCAL and DESTINATION coordinates may be reviewed by using F6 or SHIFT-F6 and pressing RETURN to leave all data unchanged. When using SHIFT-F6, the display is the same except that the title includes the word DESTINATION instead of LOCAL and you may also enter the name as "*" to set the DESTINATION coordinates to the current LOCAL coordinates. The file name shown in the example is the standard city file supplied with ASTROCLK. Using file ASTROCLK.CTY, you may automatically enter the data for any of the cities included in that file. Other "city files" may be available or may be created as required. Enter the name or first part of the name of the desired city. Only letters sufficient to unambiguously select the city are required, either upper or lower case may be used, and spaces are significant. For example, "k" is sufficient for "Kansas City" since there is ASTROCLK Astronomical Clock and Celestial Tracking Program Page 42 currently only one city beginning with the letter K, but "san f" is required to distinguish "San Francisco" from "San Antonio", "San Diego", etc. The search stops at the first match, so "san" would first match "San Antonio" and you would have to press the space bar several times before you reached "San Francisco". Alternatively, you may prefix the name you enter with the "/" character (without the quotation marks) and ASTROCLK will attempt to match your input anywhere within the file's city names. For example, a special navigation city file of VOR's, USWEST.VOR, includes the three letter code designation for each VOR in addition to the full name; the code for the Los Angeles VOR is "LAX". To select Los Angeles by the code designation, you may enter "/lax" (again without the quotation marks and in either upper or lower case). Using this method with too short or simple a designation may find many qualifying matches. For each qualifying match found, ASTROCLK presents the data read from the file and awaits your choice: SET LOCAL COORDINATES Enter CITY NAME to search for in CITY FILE: C:\ASTROCLK\ASTROCLK.CTY Enter desired name: athens ( 32) CURRENT SELECTION: Athens, GA -83 22'59.88" Longitude 33 57'24.12" Latitude 0.0 Meters (Press RETURN to ACCEPT, SPACE to find next.) The number shown in parentheses, ( 32) in the example above, shows the line number in the file. Press RETURN to ACCEPT the data shown, or press the SPACE BAR to look for the next match. Three geographical locations are "hard coded" (for my own personal convenience) and may be selected by entering the following abbreviations for the local name (upper or lower case): RPV Rancho Palos Verdes, CA CAL Calaveras County, CA USNO U. S. Naval Observatory, Washington, DC To manually enter local coordinates (instead of searching the external file), press RETURN when asked for the city name. Then enter LONGITUDE, LATITUDE, ELEVATION, and NAME when requested. WEST longitude and SOUTH latitude must be entered as NEGATIVE numbers. Press RETURN to skip an entry and leave it unchanged. As each enttry is completed, the information at the top of the window is updated. After all entries have been completed, the current local coordinates are displayed. You may append the new local coordinates to the end of the current city file by responding "Y" or "y" to the append prompt (ELEVATION is omitted for the Navigation Destination coordinates): ASTROCLK Astronomical Clock and Celestial Tracking Program Page 43 SET LOCAL COORDINATES Current LONGITUDE: -118 24'20.40" Current LATITUDE: 33 45'47.56" Current ELEVATION: 186.0 meters Current LOCAL NAME: Rancho Palos Verdes CA Append data to file [y,N]: _ You may append this location data to the current CITYFILE by pressing 'Y' or 'y'. The default response, obtained by pressing RETURN or any other key, is to NOT append the new local coordinates. The city file must already exist for the append function to execute correctly. File ASTROCLK.CTY contains the approximate longitude and latitude for about 850 selected cities in the United States and around the world. All coordinates are given in degrees to two or more decimal places and are accurate to 0.1 degrees or better in most cases. Please report any errors discovered in ASTROCLK.CTY; if you can supply the correct elevation for entries in the file, please send them in and I will update file ASTROCLK.CTY. The following examples show typical entries in file ASTROCLK.TXT: "Aberdeen, MD",-76.1617,39.5117,0 "Abilene, TX",-99.7133,32.465,0 "Akron, OH",-81.5122,41.0833,0 "Alameda, CA",-122.2433,37.7633,0 "Alamogordo, NM",-105.9567,32.9,0 "Albany, GA",-84.1583,31.575,0 "Albany, NY",-73.7503,42.6503,0 "Albany, OR",-123.0983,44.6333,0 The city or location should be enclosed in double quotation marks, as shown, followed by the longitude and latitude in degrees, and the elevation in meters. Since my sources do not include the elevation, most entries in ASTROCLK.CTY give an elevation of 0. If you know the elevation of a particular entry, use an ASCII text editor to add the elevation in meters; 1 foot equals 0.3048006 meter. NOTE: West longitudes and South latitudes are shown as, and must be entered as, as negative numbers. Use the ASCII or non-document mode in your editor and observe the comma-delimited format when making additions or changes. In addition to appending new local coordinates using F6, a special program, MAPCOORD Version 9050 or later, is available from my bulletin board system which may be used to generate city files or to append new entries to an existing city file. Other city files, including file USWEST.VOR mentioned above, are also available from time to time. Beginning with ASTROCLK Version 9050, the format for ASTROCLK city files is the same as city files for my program STSORBIT. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 44 SETTING LOCAL CONDITIONS ASTROCLK makes certain default assumptions about the current conditions when computing horizon dip (a function of the observer's elevation above mean sea level) and atmospheric refraction. These calculations are used in the Horizon (Observer) Coordinates data in Display Mode 0 and for certain navigation calculations. The default values are: Elevation: 0 meters/feet Temperature: 20 degrees Centigrade 68 degrees Farenheit Pressure: 1010 millibars 29.83 inches of Mercury If these default values are not representative of your current conditions, use ALT-F6 to set the correct LOCAL CONDITIONS. The following information will be displayed: SET LOCAL CONDITIONS Current ELEVATION: 152.4 m = 500.0 ft Current TEMPERATURE: 20.0 C = 68.0 F Current PRESSURE: 1010 mb = 29.83" The following prompts will be displayed to enable you to change each item: Enter ELEVATION (meters): Enter TEMPERATURE ( C): Enter PRESSURE (mb): For each item, press RETURN to leave that item unchanged or enter the new information. Elevation assumes the entry in meters unless you add the letter "F" to specify FEET, Pressure assumes degrees Centigrage unless you add the letter "F" to specify degrees Farenheit, and Pressure assumes millibars unless you enter a number less than 32.00 or add the letters "IN". Note that in the United States and for air traffic control, pressures are often given in hundreths of an inch, as in "2983"; this must be entered as "29.83". When all three items have been entered or accepted as is, the following prompt will appear: Press RETURN to ACCEPT, SPACE to REDO: Press RETURN to accept the entries as shown, or press SPACE BAR to start over. Since the elevation of a geographic location will probably remain constant with time, absent some major disturbance, that value is saved in the file ASTROCLK.INI and is restored each time ASTROCLK is restarted. However, the values for temperature and pressure, being quite variable, are not saved and are restored to their default values each time ASTROCLK is restarted. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 45 DUAL-TIME DISPLAYS A Dual-Time display feature is available which displays two different, selectable times in large characters in the main display window. Display Modes 1 through 5 normally display the following times in large characters in the main screen window: 1 Local Standard/Daylight Time 2 Universal Coordinated Time 3 Local Mean Sidereal Time 4 Greenwich Mean Sidereal Time 5 Terrestrial Dynamical Time (Ephemeris Time prior to 1984) Display Mode 1, Local Standard/Daylight Time, is the display mode which appears when program ASTROCLK is started. The large digit time display modes may be selected at any time by pressing the number keys 1 through 5. Use the number keys at the top of the keyboard and NOT the number keys on the numeric keypad. The title at the top of the main window gives the standard abbreviation and full name of the time displayed. To enable a dual-time display, select one of the clock display modes using the number keys 1 through 5, and then press the UP or DOWN arrow key. The normally displayed time will move up in the window and a second time will appear in yellow in the lower half of the window. Repeated pressing of the UP or DOWN arrow key will cycle through the following lower clock displays: PST/PDT Pacific Standard/Daylight Time MST/MDT Mountain Standard/Daylight Time CST/CDT Central Standard/Daylight Time EST/EDT Eastern Standard/Daylight Time TAI/A.1 International Atomic Time (after 1971) USNO Atomic Time (1958 through 1971) 5 TDT/ET Terrestrial Dynamical Time (after 1983) Ephemeris Time (prior to 1984) 4 GMST Greenwich Mean Sidereal Time 3 LMST Local Mean Sidereal Time 2 UTC Universal Coordinated Time 1 LST Local STANDARD/DAYLIGHT Time (Mode 1 only) Local STANDARD Time (Modes 2 thru 5) The UP arrow key cycles UP through the list above starting with the normal time for that display mode as indicated by the numbers at the left; the DOWN arrow key cycles DOWN through the list. Each display may be returned to the normal, single-time mode by pressing the HOME key. Note that the first five times listed can ONLY be displayed in large digits by using the DUAL TIME method. The first four times are for the standard time zones in the continental United States and will display Standard or Daylight time in agreement with the current setting of the Daylight Flag (ALT-F10). If the local time is a continental U. S. time zone, it ASTROCLK Astronomical Clock and Celestial Tracking Program Page 46 is possible to display the same time in both the upper and lower portion of the window in Display Mode 1. These times are calculated independently of the current local time zone. When the dual-time display is enabled, the abbreviation corresponding to the time displayed will also appear at the right of the time digits for each clock. For time zones in the United States, the abbreviation will change from LST (Local Standard Time) to the common U. S. abbreviation: PST for Pacific Standard Time, EST for Eastern Standard Time, HST for Hawaiian Standard Time, etc. The single or dual time selected for each of the five display modes is saved while ASTROCLK is running; changing to a different Display Mode and back again will display the same time(s). The single or dual time selected for each mode is also saved in file ASTROCLK.INI and will be restored when ASTROCLK is run the next time. Note that the Local STANDARD Time can be selected for the lower clock in Display Modes 2 through 5, whether or not the DAYLIGHT FLAG has been set. During daylight time, therefore, this display will show a different time from the small LOCAL TIME display on the right of the screen. Since some references and magazines give all times in standard time, this display will eliminate having to make the conversion if you are on daylight time. If the date has been set for 1958 through 1971, U.S. Naval Observatory Atomic Time (USNO A.1) is displayed instead of International Atomic Time (TAI). If the date has been set prior to 1958, a message in the lower portion of the window will remind the user that TAI and A.1 did not exist on the selected date. There is a slight (0.034 seconds) difference in the relationship of the two atomic time scales to TDT/ET. If the date has been set prior to 1984, Ephemeris Time (ET) is displayed instead of Terrestrial Dynamical Time (TDT). For most purposes, TDT and ET represent a continuous time scale and are treated as such by ASTROCLK; the only difference is the name displayed. There are, of course, many combinations possible. For example, you can display UTC and Local STANDARD Time, UTC and GMST, GMST and LMST, TDT and TAI, and so forth. If you are about to call the East from Los Angeles, you can display both Eastern and Pacific times, Standard or Daylight depending on the current setting of the Daylight Flag. Each of the five display modes is independent of the other four, and may be set up to display either its normal time alone, or dual time with one of the other remaining times. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 47 JULIAN DATE INFORMATION Display Mode 7, the Julian Date Information, displays a variety of date information. Press the "7" key at the top of the keyboard. The following sample illustrates the information available (DOY shown only after 1 JAN 1950): JULIAN DATE INFORMATION UTC Calendar Date: 1990 DEC 14.952188 JD Julian Date -4713 JAN 1.5 2448240.452188 MJD Julian Date 1858 NOV 17.0 48239.952187 DJD Julian Date 1900 JAN 0.5 33220.452187 TJD Julian Date 1968 MAY 23.0 8239.952187 JED Julian Ephemeris Date 2448240.452852 JE Julian Epoch 365.25 days J1990.952641 BE Besselian Epoch 365.2422 days B1990.953725 DOY UTC Day-of-Year NORAD Format 90348.952188 LOCAL Day-of-Year & Date: 348 1990 DEC 14 LOCAL Day-of-Week & Day: 6 Friday LOCAL Year/Week Code: 9050 The abbreviations used in the Julian Date lines refer to the following: JD True Julian Date referenced to -4713 JAN 1.5. This is the standard astronomical date reference. MJD Modified Julian Date referenced to 1858 NOV 17.0, often used by NASA to reduce the number of digits required. NOTE: The MJD day begins at midnight instead of noon. MJD = JD - 2400000.5. DJD Dublin Julian Date referenced to 1900 JAN 0.5, used by astronomers and mathematicians to reduce the number of digits required. DJD = JD - 2415020. JED Julian Ephemeris Date, True Julian Date (JD) corrected for Ephemeris Time (ET) or Terrestrial Dynamical Time (TDT), as appropriate. DOY UTC year, expressed as (YEAR MOD 100) * 1000, plus UTC day of the year plus UTC time expressed as a fraction of a day. This format is used by NORAD to denote dates and times in the standard 2-line orbital element sets which NORAD provides via NASA GSFC and which is required for satellite tracking programs such as STSORBIT and TRAKSAT. The more conventional day of the year format sometimes used by astronomers may be obtained by removing the two left-most digits (90348.952188 becomes 348.952188) but in this case the year must be specified inde- pendently. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 48 ALARM AND INTERVAL TIMER OPERATIONS ASTROCLK includes alarm and interval timer functions which operate independently of the program's clock modes. That is, the alarm and interval timer ALWAYS use the computer's internal clock for their operations, even with the ASTROCLK clocks off or in the simulation mode. The correct alarm and interval times, referenced to the computer's internal clock (Local Time), are therefore displayed in all clock modes. The interval timer window is displayed at all times at the lower center of the screen, but the alarm window is only displayed at the lower right of the screen when an alarm is active. Using the ALARM Function The alarm function allows the user to set an alarm to any time within the next 23 hours using either Local or UT Time. When an alarm is active, the program opens a small Alarm Window at the lower right corner of the display screen which displays the selected alarm time in the left side of the window and the coundown time, or time remaining until the alarm, in the right side of the window. The color of the countdown time changes as the local time approaches the selected time, from gray to white to yellow to blinking yellow. To set or change the alarm time, press Function Key SHIFT-F3 and enter the desired Local or UT Time in the format HH:MM:SS, HH:MM or HH.HHH, using the same flexible format rules as for setting the program time. If you prefer, use the comma instead of the colon for the separator between units. Add the letter "U" if the alarm time you are entering is UT Time; ASTROCLK will automatically convert the UT Time to Local Time and the Local Time will be displayed in the Alarm Window. If an alarm time has already been set and you wish to clear it, press SHIFT-F3 and then simply press RETURN instead of entering a time. Once an alarm time has been set using Function Key SHIFT-F3, the alarm countdown time (the time remaining until the selected alarm time is reached) may also be displayed in the main display window by pressing the letter "A" on the keyboard. The small window at the lower right of the display screen will still show both the selected alarm time and the countdown time. If no alarm time has been set, pressing the letter "A" will have no effect. The alarm function remembers the prior main window display function; if the alarm countdown time is displayed in the main display window when the alarm time is reached, the main display will automatically revert to the prior function. As further described below, the interval timer can also be synchronized to the time an alarm occurs. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 49 Using the INTERVAL TIMER ASTROCLK includes an interval timer function, measuring elapsed time rounded to the nearest second. The current value of the interval timer is always shown in the TIMER window at the lower center of the display in the format 00 00:00:00, corresponding to days and hours:minutes:seconds. The TIMER window allows times from +9999 days to -999 days; the days portion will be blanked if the day count falls outside this range. When the Interval Timer is displayed in the main display window using the "T" command, the range for that display is from +999 days to -99 days; the main window display should not be used outside this range as the interval time will NOT be updated. The interval timer display in the TIMER window is white (gray) when the timer is OFF, and yellow when the timer is ON. The following keys are used to control the operation of the interval timer: T Display interval timer in main display window S Start/Stop the interval timer without reset Z Stop and reset the interval timer PgUp Increment the interval timer DAYS PgDn Decrement the interval timer DAYS NOTE: The PgUp and PgDn keys are only active when the interval timer is displayed in the main display window using the "T" command. The interval timer may be started by one of three methods: manually, by pressing the letter "S"; automatically, when an alarm time occurs AND the interval timer is not already ON; or by setting the interval timer starting time with Function Key SHIFT- F3. When the interval timer is started automatically or by setting its starting time, it starts at zero. Note that the interval timer will NOT be automatically reset and started by the alarm function if it is already ON; in this case the interval timer will be unaffected by alarm operations. The interval timer starting time may be set using Function Key SHIFT-F3. Enter the desired starting time followed by the letter "T". If the entered time is later than the current time, ASTROCLK assumes the prior day. The total elapsed time will therefore always be less than 24 hours. To adjust the starting DAY, set the desired starting time, display the interval timer in the main display window using the "T" command, then use the PgUp and PgDn keys to set the days. Press the letter "S" to start or stop (but not reset) the interval timer. The timer may be stopped and started as often as desired whether or not the interval timer is displayed in the main display window. Press the letter "Z" to stop the interval timer and reset the accumulated time to zero. When the interval timer is displayed in the main display window and the timer is stopped, the words "TIMER IS HOLDING" will flash at the bottom of the window. The status of the interval timer is saved when ASTROCLK is ASTROCLK Astronomical Clock and Celestial Tracking Program Page 50 halted. If the interval timer is active when the program is halted, it will resume operation when next the program is started and the correct elapsed time interval (including days) will be displayed. If the interval timer is stopped but not reset when ASTROCLK is halted, the current elapsed time will be restored and the interval timer will be stopped when next the program is started. Beginning with versions 91xx (when the AUTO mode for the DAYLIGHT FLAG was added), the interval timer will automatically adjust for changes made in the DAYLIGHT FLAG. This adjustment is made for both automatic and manual changes. Note, however, that the interval timer uses LOCAL time and that changes made to the local time zone will NOT be taken into account by the interval timer. Similarly, if you are setting the interval timer for a past date (intending to use PgUp key to correct the day count) and the state of the DAYLIGHT FLAG is different now than it was then, you must make the correction when entering the start time. Linked ALARM & INTERVAL TIMER Operation If the interval timer is stopped and reset when the alarm time occurs, the interval timer will auotmatically start at the alarm time. The alarm and the interval timer then function together as a count-down-then-count-up timer. A typical operation in this manner may best be illustrated by an example. I used this arrangement during the launch of the Space Shuttle DISCOVERY on September 29, 1988 and throughout the four day mission. Prior to the mission I checked the system clock using radio station WWV from the National Bureau of Standards. To set up ASTROCLK correctly, I pressed "Z" to stop and reset the interval timer (so that it displayed 00 00:00:00), next entered the scheduled lift-off time on the alarm using Function Key SHIFT-F3, then pressed the letter "T" to display the interval timer (to establish the "prior display mode" for the alarm func- tion), followed by the letter "A" to display the alarm countdown time. ASTROCLK displayed the countdown time until lift-off and then automatically switched the main display to the interval timer to show Mission Elapsed Time (MET) throughout the four day mission. The main display may be switched to other display func- tions without affecting the accuracy of the countdown or elapsed times. Once the interval timer has started, ASTROCLK may be halted and restarted and the time will be preserved. Since the interval timer can continue for up to 9999 days (999 days when using the main window for timer display), any mission or other event of reasonable duration can easily be handled. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 51 TARGET TRACKING DISPLAY One of the problems that inspired program ASTROCLK in the first place was my inability to figure out where a star or planet could be located in the night sky even if I knew its equatorial coordinates, the right ascension and declination. These coordinates have to be converted to horizon coordinates, also known as observer coordinates, in order to relate the position of a star with my own position and the time. (Of course, I had to know the direction of true North as well, but even I could usually find Polaris without excessive difficulty.) Display Mode 0, the Target Tracking Display, provides this information in real time for both stars and planets -- although there are significant computational delays associated with the planetary positions if the micro-computer does not have a math coprocessor. The default target is Polaris, the North Star, which I have assigned the number zero in ASTROCLK's internal star database. Use Function Key F5 to select other celestial objects for tracking. Pressing "P" while in the Target Tracking Display will request the planet to track and then automatically calculate and display the position data for the planet. When already in Display Mode 0, the Target Tracking Display, pressing the "0" key again toggles between the full display (as described in the following paragraphs) and a large digit display showing the Horizon Coordinates for the target, with the APPARENT ALTITUDE on the top line and the AZIMUTH on the bottom line. The format will change with Function Key F7 (see below). However, the precision of the large digit display is two digits fewer than the full (text) display due to restricted display space. The following sample display shows the information available in the Target Tracking Display. The degree symbol, which appears in the actual display, has been deleted from the sample because of the differences among printers. 0 - a Ursae Minoris - Polaris ----------------------------- EQUATORIAL COORDINATES [J2000.0]: RIGHT ASCENSION: 2:31:48.70 DECLINATION: 89 15'50.72" HOUR ANGLE (hours): 17:07:49.20 APPARENT COORDINATES [J1988.9]: RIGHT ASCENSION: 2:20:08.44 DECLINATION: 89 12'51.34" HOUR ANGLE (hours): 17:19:29.45 OBSERVER HORIZON COORDINATES: ALTITUDE: 33 37'33.09" AZIMUTH (NESW): 0 55'44.18" Apparent ALTITUDE: 33 38'57.11" [Charts SA=1 U=I-1] [VMag = 2.02] The Equatorial Coordinates are first shown for the current epoch of the internal star database; the default is J2000.0, as shown in the sample above. These data are "mean" positions for ASTROCLK Astronomical Clock and Celestial Tracking Program Page 52 the epoch shown, as found in typical star catalogs. The Apparent Coordinates are the apparent geocentric equatorial coordinates which have been (for stars) precessed and corrected for proper motion, nutation, and annual aberration but NOT parallax, or (for planets) calculated as of the mean equinox of date, J1988.9 in the sample. The stellar apparent geocentric equatorial coordinates agree with the Astronomical Almanac and the USNO Interactive Computer Ephemeris to an accuracy of typically less than one second of time or arc; planetary data are less accurate. Versions of ASTROCLK prior to 8847 displayed "apparent coordinates" which were the current star database coordinates adjusted for refraction. The present display is in keeping with the accepted definition of "apparent" (that is, referenced to the mean equinox of date), and the coordinates have NOT been corrected for refraction. The local HA (Hour Angle, hours) is related to the RA (Right Ascension, hours) and LMST (Local Mean Sidereal Time, hours) by the formula: HA = LMST - RA Technically, the LAST Local Apparent Sidereal Time should be used, but I have compromised, as have some of my sources, since the difference is small (on the order of 0.2 seconds in 1988) and many calculations can thereby be avoided; while not particularly important if your computer has a math coprocessor, the delay may be significant if it does not. The Horizon (or Observer) Coordinates are referenced to the current ASTROCLK local geographical coordinates. The Altitude is the angle above the true horizon, and the Azimuth is the angle from true North, measured in the sense NESW. Thus, North is 0 degrees, East is 90 degrees, South is 180 degrees, and West is 270 degrees. The Apparent Altitude is the Altitude corrected for atmospheric refraction and horizon dip (if the local elevation is non-zero); Azimuth is unaffected by refraction. The approximate visual or photographic magnitude of the object is shown at the lower right of the window border, marked as "VMAG" (visual magnitude) for stars and planets or "BMAG" (blue/photographic magnitude) for minor planets. The values for stars are constant values from the internal or external catalog while those for planets and minor planets are calculated approximations for the current time and date. The chart numbers in two of the most commonly used star atlases are shown for the target object in the Chart data at the lower left of the target window. "SA=" gives the chart number in Sky Atlas 2000.0 and "U=" gives the volume(s) and chart number for Uranometria 2000.0. Of course, the target object may or may not appear on the chart, depending upon the type of object and its magnitude; planets, for example, will not appear because of their constantly changing positions. Even when the object does not appear on the chart, however, the chart for the proper area may be useful to establish neighboring stars, the constellation name, etc. The original algorithm used to calculate the chart numbers was published in Sky & Telescope Magazine in April 1989; ASTROCLK Astronomical Clock and Celestial Tracking Program Page 53 the algorithm has been substantially modified and converted to QuickBASIC for use in ASTROCLK. Function Key ALT-F7 changes some of the units used for the Target Tracking Display, as shown in the following sample (and again, the degree symbol has been deleted). 0 - a Ursae Minoris - Polaris ----------------------------- EQUATORIAL COORDINATES [J2000.0]: SIDEREAL HR ANGLE [SHA]: 322 02'49.43" DECLINATION [DEC]: 89 15'50.72" GREENWICH HR ANGLE [GHA]: 15 21'29.95" APPARENT COORDINATES [J1988.9]: SIDEREAL HR ANGLE [SHA]: 324 57'53.18" DECLINATION [DEC]: 89 12'51.34" GREENWICH HR ANGLE [GHA]: 18 16'33.70" OBSERVER HORIZON COORDINATES: ALTITUDE [Hc]: 33 37'33.09" AZIMUTH (NESW) [Zn]: 0 55'44.18" Apparent ALTITUDE [Ho]: 33 38'57.11" [Chart SA=1 U=I-1] [VMag = 2.02] This alternate form of the Target Tracking Display shows the same basic information as above, but in a form preferred by navigators. Press ALT-F7 again to return to the original format. SHA (Sidereal Hour Angle, degrees) is related to RA (Right Ascension, hours) by the formula: SHA = 360 - RA * 15 GHA (Greenwich Hour Angle, degrees) is related to SHA (Sidereal Hour Angle, degrees) and GAST (Greenwich Apparent Sidereal Time, hours) by the formula: GHA = 15 * GAST + SHA Not shown but also occasionally required is LHA (Local Hour Angle, degrees) which is obtained using the following formula: LHA = GHA + Longitude The abbreviations shown in square brackets [...] are those given in the Nautical Almanac and the USNO Almanac for Computers for use in navigation. Note that in this mode, the Apparent Altitude will show the abbreviation [Ho] if the local elevation is zero, and [Hs] if the local elevation is non-zero. [Ho] refers to the "observed" altitude after corrections for horizon dip and instrument error, while [Hs] refers to the "sextant" altitude after correction for instrument error but as measured to the actual horizon. If the navigational instrument being used provides its own artificial horizon, set the local elevation to zero. Function Key F7 may be used to change the units used in the Target Tracking Display. Three different formats for time and ASTROCLK Astronomical Clock and Celestial Tracking Program Page 54 degrees are available; press F7 to cycle through the formats: ANGLES TIME ------------ ----------- DDD MM SS.SS HH:MM:SS.SS DDD MM.MMMM HH:MM.MMMM DDD.DDDDDD HH.HHHHHH However, note that the large digit display (showing Apparent Altitude and Azimuth) and obtained by pressing the "0" key when in the Tracking Data Mode, displays the data to lower precision due to screen space restrictions. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 55 TARGET OBJECT EPHEMERIS Quite a number of ASTROCLK users have requested the capability of displaying and/or printing an ephemeris, a listing of the position of a celestial object for a series of specific dates and times. While ASTROCLK was intended more as a real time clock and tracking program than for the generation of tabular data, it is admittedly very useful to be able to produce such a listing in anticipation of an evening with behind your telescope. Because of increasingly severe memory constraints, direct printing is not possible with this version of ASTROCLK except by using the SHIFT-PrtSc key. However, Function Key F2 now displays an ephemeris for the current target object, replacing the previous function of cycling through the various clock displays. Before pressing Function Key F2, ASTROCLK must be set up for the desired target object (star, planet, minor planet, etc.) using Function Key F5. For most objects outside the solar system, of course, the position will change very slowly with time. Next set the desired starting time using Function Key F3. Two additional items are required before the ephemeris can be displayed, the step interval (the time from one calculation to the next) and the number of intervals. SET TARGET EPHEMERIS PARAMETERS The ephemeris will be generated for the current TIME and DATE. Use F3 to change. Enter INTERVAL [1 day]: Enter the ephemeris step interval in DAYS, or: Add 'Y' or 'y' for 365-day YEARS. Add 'H' or 'h' for HOURS. Add 'M' or 'm' for MINUTES. The default units for the interval are DAYS; simply enter the number of days between steps and press RETURN. If you wish other units, 365-day years, hours, or minutes, add the letter Y, H, or M (upper or lower case) respectively following the number. Enter number of intervals [10]: Then enter the total number of intervals desired or press RETURN for 10 intervals. ASTROCLK will generate the ephemeris with 20 lines per display screen. When the complete ephemeris has been displayed and each time the screen fills, the program will pause so that you may read or print the information. Press any key to continue. After the ephemeris is completed, ASTROCLK will resume normal operation. The following is a sample ephemeris generated for the planet Neptune on August 30, 1989 with an interval set to one day and ten intervals requested: ASTROCLK Astronomical Clock and Celestial Tracking Program Page 56 ASTROCLK EPHEMERIS FOR: Planet #8 NEPTUNE (Automatic) Equinox of Date [J1989.6] Julian Date Local Date PDT Time Rt. Ascen. Declination 2447769.478183 30-08-1989 16:28:35 18:42:04.82 -22 10'38.63" 2447770.478183 31-08-1989 16:28:35 18:42:02.00 -22 10'43.65" 2447771.478183 01-09-1989 16:28:35 18:41:59.31 -22 10'48.61" 2447772.478183 02-09-1989 16:28:35 18:41:56.75 -22 10'53.43" 2447773.478183 03-09-1989 16:28:35 18:41:54.31 -22 10'58.11" 2447774.478183 04-09-1989 16:28:35 18:41:52.00 -22 11'02.67" 2447775.478183 05-09-1989 16:28:35 18:41:49.83 -22 11'07.07" 2447776.478183 06-09-1989 16:28:35 18:41:47.79 -22 11'11.35" 2447777.478183 07-09-1989 16:28:35 18:41:45.90 -22 11'15.52" 2447778.478183 08-09-1989 16:28:35 18:41:44.13 -22 11'19.54" As usual in these text examples, the degree symbol has been omitted because of printer differences, and the right-most column, giving the object's magnitude, has been deleted because of space limitations; the value was 7.89 and 7.90 for the dates shown. The Local Date and Time are based upon the current geographical coordinates and time corrections (DAYLIGHT FLAG and ZONE CORRECTION); the time zone abbreviation, PDT in the example, is also included. Note that the coordinates shown are the Apparent Geocentric Equatorial Coordinates for the Epoch and Equinox of Date, J1989.6 in the example. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 57 PRECISION TIME AND DATA DISPLAYS The ASTROCLK on-screen clocks on the right portion of the screen display times rounded the nearest second. It is sometimes useful to view the various times and other parameters to a higher precision. Display Mode 8 provides this facility with six preci- sion displays: two Precision Time Displays, three Precision Data Displays, and one local Sunrise/Sunset & Twilight display. Switch between the displays with the PgUp or PgDn keys, or press the "8" key. When ASTROCLK exits, the current Precision Time/Data Display window is saved; that window will appear when Display Mode 8 is next selected. When ASTROCLK is first executed, this mode shows Precision Time Display #1 with all times shown to a precision of 0.0001 seconds. Note, however, that the displayed precision may be greater than the accuracy of the calculations as discussed below. The limitations of a microcomputer and the available software become apparent as more complex calculations are attempted. Given unlimited execution time and appropriate software, of course, there is no reason why the microcomputer cannot produce data to any desired accuracy. However, the real world imposes certain constraints and the complex mathematics of practical astronomy forces compromises. Even with a math coprocessor, the calculation times are noticeable; without the math coprocessor they are significant. The Precision Data Displays show various intermediate parameters required for the calculation of some of the basic astronomical quantities. Each is an important item in its own right, but in the context of a program such as ASTROCLK, its function is more nearly that of the building block needed to construct the whole. Readers are again reminded that the precision of the displayed data is generally greater than its accuracy; the higher precision has been retained as a testing tool as the program's accuracy is gradually increased through improved algorithms and technique. The sample displays were all generated at 00:00:00 UT for 4 November 1988. The Daylight Flag was OFF and the Local Coordinates were set for Calaveras County, near Sacramento, in Northern California (preset location "CAL"). As an additional feature, the UP and DOWN arrow keys may be used to increase or decrease the Julian Date by one day when using the precision displays in Display Mode 8, but ONLY when the clocks are OFF; use Function Key F4 to start and stop the clocks. The UT time remains constant, but all other data are recalculated. I have used this feature while comparing the ASTROCLK calculations against tabulated data; how useful it may otherwise be is questionable. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 58 Precision Time Display #1: -------------------------- UTC Coordinated Universal Time: 0:00:00.2404 UT Universal Time (=UT1): 0:00:00.0000 TAI International Atomic Time: 0:00:24.2404 TDT Terrestrial Dynamical Time: 0:00:56.4244 Gwich Mean Solar Time (UT): 0:00:00.0000 Greenwich App. Solar Time: 0:16:24.2747 GMST Grnwich Mean Sidereal Time: 2:57:45.7030 GAST Grnwich App. Sidereal Time: 2:57:45.9618 GSD Greenwich Sidereal Date: 2454172.123446 NOTES: For the period 1958 through 1971, A.1 USNO Atomic Time will be shown in place of TAI International Time. Prior to 1984, ET Ephemeris Time will be shown in place of TDT Terrestrial Dynamical Time. The basic time reference for all internal ASTROCLK time calculations is Universal Time (UT), whether derived from the computer's internal clock or entered manually. This time is therefore considered to be exact and accurate to the full precision shown and is the same as UT1. Universal Coordinated Time (UTC), which is the time broadcast by radio stations WWV, WWVH, and most other radio time standards, is kept to within 0.9 seconds of UT by the occasional insertion of Leap Seconds at the end of June or December. Except for this Precision Time Display, which shows the calculated or estimated difference between UT and UTC, ASTROCLK otherwise assumes UT for all time calculations. International Atomic Time (TAI) has been officially recognized as an official time standard since 1972 although the U.S. Naval Observatory has provided an atomic time standard since 1958. The difference between TAI and UTC is published in the Astronomical Almanac for years 1972 and up. For the period 1958 through 1971, ASTROCLK calculates USNO Atomic Time (A.1). The difference between A.1 and UTC ranges from 0 to 10 seconds and ASTROCLK assumes a linear rate of change with one second increments added on January 1 or July 1 when appropriate. The offset between TAI and A.1 versus TDT/ET is slightly different: 32.184 seconds versus 32.15 seconds respectively. Prior to 1958, ASTROCLK does not display an atomic time. Terrestrial Dynamical Time (TDT) and its pre-1984 cousin Ephemeris Time (ET) are calculated for the period 1620 through 1989 based upon data published in the Astronomical Almanac. Outside that period a formula by Meeus, adjusted slightly to merge smoothly with the data in the Astronomical Almanac, has been used (see BIBLIOGRAPHY). The Astronomical Almanac advises that for most purposes ET and TDT may be considered a continuous time standard. ASTROCLK uses the appropriate designation, ET or TDT, depending upon the current date but otherwise makes no distinction between them. Terrestrial Barycentric Time (TBT) is never more than 1.7 milliseconds different from TDT and is not shown; for most calculations the two may be considered the same. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 59 ASTROCLK's calculation of Greenwich Mean Sidereal Time (GMST) has been compared with the published Astronomical Almanac data for the year 1988 and agrees to the full precision shown, 0.0001 seconds. However, Greenwich Apparent Sidereal Time (GAST) involves many more calculations and the accuracy falls off to approximately 0.01 seconds. Precision Time Display #2: -------------------------- PST Local Standard Time: 16:00:00.0000 Local Mean Solar Time: 15:57:43.9999 Local App. Solar Time: 16:14:08.2747 LMST Local Mean Sidereal Time: 18:55:29.7029 LAST Local App. Sidereal Time: 18:55:29.9617 Equation of Time: + 0:16:24.2747 Delta T (TDT/ET-UT): 0:00:56.4244 Delta AT (TAI-UT): 0:00:24.0000 For locations within the United States as well as for other areas falling in the same time zones, the abbreviation PST will be replaced by the abbreviation appropriate for the local time zone. In addition, the middle letter will change (S or D) depending upon whether Standard or Daylight time is in effect, as determined by the setting of the Daylight Flag. For other time zones, the abbreviation PST will be replaced by LST (Local Standard Time) or LDT (Local Daylight Time) according to the setting of the Daylight Flag. The local times shown have essentially the same accuracy as the corresponding Universal or Sidereal times (given upon the assumption that the local coordinates are exact). Thus, Local Standard/Daylight Time may be considered exact (provided the Daylight Flag and Zone Correction have been correctly set), Local Mean Sidereal Time is accurate to the precision shown, and Local Apparent Sidereal Time is accurate to approximately 0.01 seconds. Local Mean Solar Time, calculated using UT and the local longitude, is accurate to approximately the precision shown. The Equation of Time is the difference between the Right Ascension of the apparent Sun and the fictitious mean Sun. In addition to being required for various calculations, it represents the difference between mean solar time (upon which our civil timekeeping is based) and apparent solar time, the time shown by a sundial. Delta T and Delta AT show the calculated or estimated difference between UTC versus TDT/ET and TAI/A.1 respectively. Prior to 1958, Delta AT is not shown. In ancient times, Delta T can reach values greater than 24 hours; in this case, Delta T is shown as days (suffixed by "d") followed by hours as usual. The error in Delta T for ancient times is estimated to be as much as several hours. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 60 Precision Data Display #1: -------------------------- Mean Obliquity of Ecliptic: 23 26'26.63" [0.02"] True Obliquity of Ecliptic: 23 26'35.40" [0.02"] Nutation in Longitude: 0 00'04.32" [0.05"] Nutation in Obliquity: 0 00'08.76" [0.05"] Equation of Equinoxes (secs): 0.263960 [0.005 sec] e EARTH Eccentricity of Orbit: 0.01671380 L' MOON Mean Longitude: 157 55'15.39" M' MOON Mean Anomaly: 168 35'33.91" MOON Asc Node Longitude: 340 51'23.71" E Equation of Time (h:m:s): + 0:16:25.8574 T Jul Cent @ 2000 JAN 1.5 TDT: -0.111581091 @ 1900 JAN 0.5 ET: 0.888418909 NOTES: All items are expressed in degrees or time as appropriate, with the format determined by Function Key F7. In the actual ASTROCLK display, the last parameter is shown with the omega symbol usually associated with that parameter, and all items in degrees include the degree symbol. Because of the differences among printers, those symbols have been omitted in this text. The numbers in the right hand column above are the approximate accuracy of the calculations compared with data published in the Astronomical Almanac. Items with no accuracy data shown have been checked against other sources and appear to be accurate to about 0.001 degrees or 0.1 seconds or better; the MOON paramaters are used in the calculation of the first four items of the precision times and therefore probably have at least comparable accuracy. Function Key F7 may be used to change the format of the displayed data as in other display modes. In the default mode (degrees or hours, minutes, and seconds), data are displayed to a precision of 0.01 seconds of arc or time. Precision Data Display #2: -------------------------- Geocentric Data @ Equator & Ecliptic of Date: --------------------------------------------- L SUN Mean Longitude: 223 27'38.75" 0 SUN True Longitude: 221 47'42.02" 0a SUN Apparent Longitude: 221 47'27.20" M SUN Mean Anomaly: 300 42'43.97" v SUN True Anomaly: 299 02'53.02" R SUN Radius Vector (AU): 0.99167759 C SUN Equation of Center: -1 39'50.95" a SUN Apparent Rt. Ascension: 14:37:24.72 d SUN Apparent Declination: -15 22'27.89" NOTES: All items are expressed in degrees or time as appropriate, with the format determined by Function Key F7. In the actual ASTROCLK display, Right Ascension and Declination are shown with the alpha and delta symbols usually associated with those parameters, and all items in degrees include the degree symbol. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 61 This display shows the calculated values for parameters associated with the Sun. CAUTION: Depending upon the source, formulae used to calculate these and other precision data may refer T to 2000 JAN 1.5 TDT, the new standard epoch, OR to 1900 JAN 0.5 ET, the prior standard epoch. Precision Data Display #3: -------------------------- SUN Geocentric Rectangular Equatorial Coords -------------------------------------------- @ Mean Equator & Equinox of Date: X Coordinate: -0.7393294 Y Coordinate: -0.6063765 Z Coordinate: -0.2629145 @ Mean Equator & Equinox of J2000.0: X Coordinate: -0.7375287 Y Coordinate: -0.6082189 Z Coordinate: -0.2637152 The standard equator and equinox shown in the sample is J2000.0, and is always the same as that used for the internal star database. It may be set with Function Key F8 to any desired epoch using a variety of input formats. These coordinates are frequently required for Epoch B1950.0 for use with planetary and other solar system data. NASA also uses B1950.0 for most data. Solar Rise/Set & Twilight: -------------------------- SOLAR RISE/SET & TWILIGHT Morning Evening ------------------ Sunrise/Sunset 06:20:36 19:29:47 Civil Twilight: 05:52:48 19:53:41 Nautical Twilight: 05:22:07 20:24:29 Astronomical Twilight: 04:50:19 20:56:24 Calculations for: Rancho Palos Verdes CA Friday, 19 APR 1991 This display shows the local times of sunrise, sunset, and the three defined twilights, Civil, Nautical, and Astronomical. The calculation method chosen is iterative and may require a considerable amount of time on computers not equipped with a math coprocessor, on the order of 30 seconds or more. However, the calculation is only made once for a particular day and local coordinates, and thereafter the display is essentially immediate. The local times shown reflect the current setting of the DAYLIGHT ASTROCLK Astronomical Clock and Celestial Tracking Program Page 62 FLAG. As with all of the Precision Data displays, stopping the clocks with Function Key F4 permits the current day to be incremented or decremented by pressing the up or down arrow key respectively. This provides a simple method for displaying the sunrise, sunset and twilight data for the next several days. When a given phenomenon does not occur, such as sunrise and sunset during summer months in near polar regions, the time for that phenomenon will be replaced by "********" and a notation to that effect is added to the display. Calculating the time of sunrise or sunset is a chancy business at best. The Astronomical Almanac (AA) gives all times to the nearest minute on the theory that the actual time can seldom be predicted with greater accuracy given the variability of local conditions and refraction effects. I have chosen to include the seconds primarily as a starting point for my own timing measurements and not because the times are accurate to that precision. ASTROCLK's calculated times are typically the same as, or within one minute of, the times given by AA, the USNO Interactive Computer Ephemeris (ICE), and the USNO Floppy Almanac (FA) for 1991. Note, however, that ICE typically disagrees by one minute from ASTROCLK and FA (which are the same); ICE appears to use Terrestrial Dynamical Time (TDT) for these data and this may account for the one minute difference. The sunrise and sunset times take into account the horizon dip for the elevation at the local coordinates and assume a level and true horizon such as is obtained with a seaward view. Local mountains or other obstructions may significantly affect the observed times. Twilight times are calculated as defined and are not affected by local elevation. The calculated values may be checked against the AA by setting the local coordinates to a longitude of zero degrees, a latitude corresponding to the desired column in Section A of the AA, and setting the elevation to zero. Alternatively, times may be checked against ICE by setting the local elevation to zero using Function Key F6. Unlike sunrise and sunset, the various twilight times are the result of the mathematical definition of those phenomenae and are not subject to the same local variations. Each time is determined by how far the center of the Sun is located below the appropriate horizon: 6, 12, and 18 degrees for Civil, Nautical, and Astronomical twilight respectively. My thanks to Matt Merrill for his efforts in writing and debugging the original QuickBASIC code for these calculations, derived from Bretagnon and Simon, Planetary Tables, which I have adapted for use within ASTROCLK with few changes. ASTROCLK Astronomical Clock and Celestial Tracking Program Page 63 PLANETARY DATA DISPLAYS By far the most demanding task that ASTROCLK asks of the micro-computer is the calculation of the positions of the planets; it is also one of the more important tasks for the interested star gazer, since the planets are among the more distinctive objects easily seen with the naked eye. Beginning with Version 8846, ASTROCLK calculates the full planetary position at the current time (ecliptic and equinox of date), displays its results using Display Mode 9, and makes those results available to the Tracking Display, Display Mode 0. For a micro-computer without a math coprocessor, the computational delays are very significant; my Zenith Z-183, running at 8 Mhz, requires about four to six seconds per position calculation, depending upon the planet. For a micro-computer equipped with a math coprocessor, the delays are noticeable but my Zenith Z-248 IBM AT-compatible gets the job done in less than one second. When the letter "P" is pressed, or the first time Display Mode 9 is requested, ASTROCLK asks you to select a planet or minor planet for display. The major planets are assigned their "standard" numbers corresponding to their position outward from the Sun. Planet #3, the Earth, cannot be selected. A planet may be selected by entering either the planet number or the planet name. Except for Mercury and Mars, the first letter (upper or lower case) of the planet name is sufficient to select the planet; the first two letters are required to distinguish between MErcury and MArs. The letter "H" will select Comet Halley, the letter "X" will select the external Minor Planet Catalog (if present), and the letter "Z" allows manual entry of all orbital parameters. See the section MINOR PLANET SELECTION for additional information on minor planets and orbital parameters. The Planet Selection display reminds the user of the planet's numbers and names: PLANET SELECTION ---------------- Enter PLANET NAME/NUMBER: 1 = Mercury 6 = Saturn 2 = Venus 7 = Uranus 4 = Mars 8 = Neptune 5 = Jupiter 9 = Pluto H = Comet Halley (internal data) X = External Minor Planet Catalog Z = Enter Orbital Parameters - All orbital elements @ Mean Equinox of Date - Use UP and DOWN arrows to change PLANET after making initial selection. Once the initial selection has been made or at any time from another display mode, pressing "P" will allow you to select a planet or minor planet and will automatically select Display Mode 9 unless you are in the Tracking Display, Display Mode 0. While displaying planetary data in Display Mode 9, pressing the UP ASTROCLK Astronomical Clock and Celestial Tracking Program Page 64 arrow will cycle through the planets (but not the minor planets!) moving outward from the Sun and pressing the DOWN arrow will cycle through the planets moving inward toward the Sun. The position of the selected planet is calculated in several stages using the current time. First, current position data for the Sun are calculated (as in the Precision Data Display), then the orbital elements for all planets are determined for the instant of interest. Next, the heliocentric (Sun-centered) and geocentric (Earth-centered) ecliptic coordinates for the requested planet are found and corrected for perturbations of the other planets. Finally, the geocentric ecliptic coordinates are converted to equatorial coordinates, the more familiar Right Ascension and Declination. All data to this point are calculated for the mean equinox of date, which appears as the Julian Epoch at the right side of the window border for Display Mode 9 in the form "[J1988.9]". The internal star database is always referenced to a particular epoch; the current star database epoch is always shown in Display Mode 0. The default star database epoch is J2000.0 and it may be changed using Function Key F8. For consistency, therefore, the planetary equatorial coordinates are also automatically precessed to the current star database epoch and then preset as the current target for use in Display Mode 0, the Tracking Display. Therefore, having determined the current coordinates for the selected planet, the user may change to the Tracking Display and monitor the planet's position in equatorial and horizon (observer) coordinates. Selecting a planet from the Tracking Display directly by pressing "P" bypasses the Planetary Data Display and shows the tracking data immediately. Once a planet has been selected by using "P" or Display Mode 9, the data is always available to the Tracking Display UNLESS you select a star or other celestial object for display in the meantime. If you have selected a star for display, you must again select a planet with "P" before its data will be shown in the Tracking Display. Because of the additional computational delays for the "average" micro-computer when processing a planet's equatorial coordinates in the Tracking Display, Display Mode 0, the user may notice a significant "slow down" in the Tracking Display as compared to the performance when a star or other fixed celestial object is being tracked. The additional calculations related to planetary position are only performed when a planet is selected for display. Two display screens are available for the selected planet in Display Mode 9: Planetary Data (default) and Orbital Data. Pressing the PgUp, PgDn, or "9" keys will switch between the two displays. The sample displays shown below were taken for MARS at 00:00 UT on 8 November 1988 and ASTROCLK's star epoch was J2000.0. As with other ASTROCLK data, the reader is reminded that the accuracy of the data is not necessarily as good as the precision displayed; this is particularly true of the planetary data, given the complexity of the calculations. See the section PRECISION AND ACCURACY TESTS for additional discussion. Because of the differences among printers, the degree symbol (which appears on the displays) has been deleted from all sample ASTROCLK Astronomical Clock and Celestial Tracking Program Page 65 displays, and the symbols omega and theta zero have been deleted for the Longitude of the Ascending Node and the Angular Diameter at 1 AU, respectively, in the Orbital Display. MARS Planetary Data [J1988.9] ------------------------------------------------------- Heliocentric Longitude: 29 59'44.09" Heliocentric Latitude: -0 37'00.40" Heliocentric Radius (AU): 1.4320914 Appar Geocentric Longitude: 0 34'28.42" Appar Geocentric Latitude: -1 36'23.79" Geocentric Distance (AU): 0.5498746 Apparent Right Ascen [J1988.8]: 0:04:41.06 Apparent Declination [J1988.8]: -1 14'36.50" Apparent Right Ascen [J2000.0]: 0:05:15.32 Apparent Declination [J2000.0]: -1 10'53.20" Ang Size (") & Vis'l Mag: 17.02 -1.97 The Heliocentric Ecliptic Longitude, Heliocentric Ecliptic Latitude, Heliocentric Radius, and Geocentric Distance are the instantaneous values corrected for perturbations but not for light time; they are therefore the true values for the given instant. The Geocentric Ecliptic Longitude and Geocentric Ecliptic Latitude have been corrected for perturbations, light time, nutation, and aberration and are therefore the apparent values for the given instant. The two sets of equatorial coordinates, apparent right ascension and apparent declination, are calculated for two different epochs. The first set is calculated for the current time and date and is therefore for the Mean Equinox of Date (J1988.9 in the samples, also shown at the upper right of the window border). The values for the second set of equatorial coordinates have been precessed to the current epoch for ASTROCLK's internal star database; the default epoch for the internal star database is J2000.0, as shown in the sample above. Precessing the internal star database using Function Key F8 will change the epoch used for these coordinates. It is this last set of coordinates, referenced to the current star database epoch, which is automatically transferred to Display Mode 0, the Tracking Display, where the same data is displayed, and is converted to horizon coordinates and corrected for refraction. The apparent size in arcseconds and the approximate visual magnitude are shown on the last line of the display. Care must be taken when comparing ASTROCLK's planetary data with other sources to ensure that the data are calculated for the same time, date, and epoch. For example: the Astronomical Almanac and the USNO Floppy Almanac use Terrestrial Dynamical Time (TDT) and provide positions as of the Mean Equinox of Date; Bretagnon and Simon use UT (internally converted to TDT/ET) and calculate positions as of the Mean Equinox of Date but use the Zero Year date numbering system for years "BC"; Sky & Telescope Magazine provides sample planetary data each month which is calculated using Universal Time (0 hours UT) and the Mean Equinox of Date; and, Astronomy Magazine does not specify a time scale or time for ASTROCLK Astronomical Clock and Celestial Tracking Program Page 66 its monthly planetary calculations but data is marked Epoch J2000.0. MARS Orbital Data [J1988.9] ------------------------------------------------------- L Mean Longitude: 21 40'41.18" _ Mean Daily Motion in Long: 0 31'26.65" w Longitude of Perihelion: 335 51'13.93" e Eccentricity: 0.09339464 i Inclination: 1 50'59.08" Longitude of Asc Node: 49 28'17.35" a Semi-Major Axis (AU): 1.52368830 Ang Diameter @ 1 AU (arcsecs) 9.36 Std Visual Magnitude [V(1.0)] -1.52 The Mean Longitude, Longitude of Perihelion, Eccentricity, Inclination, Longitude of the Ascending Node, and the Semi-Major Axis are the six standard orbital elements used for calculating the instantaneous position of a planet in its orbit about the Sun. [NOTE: Some authors use the Argument of the Perihelion instead of the Longitude of the Perihelion.] The Mean Daily Motion in Longitude is derived from the Mean Longitude as a function of time. The Angular Diameter at 1 AU is the standard angular diameter measured at a distance of 1 Astronomical Unit. Similarly, the Standard Visual Magnitude shown is the standard visual magnitude measured at a distance of 1 Astronomical Unit. The calculation of the positional data for a selected planet requires first that the orbital elements for all planets be calculated. The orbital elements are then used to compute the perturbations affecting the selected planet. Only the orbital elements for the selected planet are shown in the Orbital Data Display and only the last three items in the display are constants. All other data must be re-computed for each instant. After a planet has been selected, switching to the Tracking Display, Display Mode 0, will show the usual tracking data for the selected planet updated once per second or as rapidly as the micro-processor can manage (degree symbol deleted): P4 MARS (Automatic) --------------------- EQUATORIAL COORDINATES [J2000.0]: RIGHT ASCENSION (hours): 0:05:15.32 DECLINATION (degrees): -1 10'53.20" HOUR ANGLE (hours): 19:10:42.68 APPARENT COORDINATES [J1988.8]: RIGHT ASCENSION (hours): 0:04:41.06 DECLINATION (degrees): -1 14'36.52" HOUR ANGLE (hours): 19:11:16.94 OBSERVER HORIZON COORDINATES: ALTITUDE [Hc] (degrees): 14 01'20.61" AZIMUTH [Zn] (degrees): 101 10'41.66" Apparent ALTITUDE (degrees): 14 04'59.95" [Charts SA=17 U=I/II-215] [VMag = -1.97] ASTROCLK Astronomical Clock and Celestial Tracking Program Page 67 MINOR PLANET SELECTION The current complete Minor Planet Catalog as of this writing, ELEM1989.001 for March 15, 1989 compiled by E. G. Bowell of the Lowell Observatory, lists 3,774 minor planets and their various orbital parameters. This is far too much data for direct inclusion in ASTROCLK; in conventional ASCII format, the full Minor Planet Catalog requires over 380K bytes of disk storage. In addition, reading the ASCII data and converting the parameters to the internal numerical formats required by ASTROCLK requires extra computational time. I have therefore designed a compressed Minor Planet Catalog format for use with ASTROCLK; the compression to ASTROCLK's MPC format, along with data examination and recreation of the original ASCII format, if desired, is performed by program MPCAT. The resulting MPC format file, ELEM891.MPC, requires approximately 241K bytes for the full catalog, still quite a bit if you don't happen to be interested in minor planets. Therefore, an abbreviated version of the full catalog, ASTROCLK.MPC, containing the first 250 minor planets is included with the standard distribution of ASTROCLK and only requires approximately 64K bytes. The full MPC catalog is available from my bulletin board system. (See A BRIEF EDITORIAL for further information.) Unlike the major planets, no "general theory" exists for the complex motion of the many minor planets; these smaller bodies are not only subject to the influence of the major planets but interact with each other -- and there are thousands of them in the so-called "asteroid belt". There are therefore no handy time- dependent equations which will yield orbital and position information over long time spans. Instead, so-called "osculating elements", accurate for a specific date (the "epoch" of the data) and referred to a specific ecliptic and equinox (the "standard describe the orbit of each minor planet. Most minor planet data is referenced to the standard epoch of B1950.0, although some publications including the Astronomical Almanac now use J2000.0. When processing minor planet data, ASTROCLK first reduces the raw osculating elements as read from the Minor Planet Catalog in use to the equinox of date (based upon the current epoch set in ASTROCLK for the internal star database), then performs all of the various orbit and position calculations as of the ecliptic and equinox of date. The data is then processed in the same manner as for the major planets, taking into account light time and yielding the apparent position for the equinox of date. The data are also precessed to the current standard epoch, but readers are cautioned that these data are also the APPARENT position rather than the ASTROMETRIC position. In particular, the Astronomical Almanac data for selected minor planets (Section G) are astrometric as of Epoch J2000.0 and will therefore not agree precisely with those generated by ASTROCLK. As the date of interest moves further from the catalog date, the position calculations become progressively less accurate. When possible, use a minor planet catalog which is valid for a date near (within several months, for example) the date of ASTROCLK Astronomical Clock and Celestial Tracking Program Page 68 interest. ASTROCLK displays the osculation date for the external catalog in the form DD-MM-YYYY, but no check is made for excessive time spans. See also the section PRECISION AND ACCURACY TESTS for further discussion. Before attempting to use the Minor Planet Catalog, use Function Key ALT-F10 to verify that the path and file name for the catalog are set correctly. Particularly if you are upgrading from a previous version of ASTROCLK, the file name and path will probably be incorrect. As with the major planets, selection of a minor planet begins by pressing the letter "P" for Planet Selection, then press "X" to select the Minor Planet Catalog. Information about the catalog is then displayed and the minor planet number is requested: MINOR PLANET SELECTION Minor Planet SOURCE file: ELEM1989.001 [SOURCE: E G BOWELL, LOWELL OBSERVATORY] Minor Planet CATALOG file: ASTROCLK.MPC Minor Planet Data Date: 15-03-1989 Minor Planet Ecliptic Date: B1950.0 First Minor Planet: 1 Last Minor Planet: 250 Total Minor Planets: 250 Enter Minor Planet NUMBER: [Press RETURN to enter NAME] Enter the desired minor planet number, followed by RETURN, or press RETURN alone and receive the prompt to enter the minor planet name: Enter Minor Planet NAME: [Press RETURN to cancel] Enter the desired minor planet name, followed by RETURN, or press RETURN again to cancel the name request and return to the main Minor Planet Selection menu. When entering a minor planet name, upper or lower case may be used and only sufficient letters are required to unambiguously identify the desired minor planet. For example, to search for VICTORIA you might enter simply "VIC" or "vic". ASTROCLK will search the catalog for any minor planets whose name begins with the letters VIC. When possible, use the minor planet NUMBER rather than the minor planet NAME. ASTROCLK can retrieve the data directly when the number is given, but must search through the entire file looking for a match to the name. Depending upon the type and speed of your disk system, the time difference can be very considerable! Once ASTROCLK has located the requested minor planet or one which matches the requested name, the data for that minor planet is displayed: Minor Planet 12: VICTORIA Ecliptic Epoch: B1950.0 ASTROCLK Astronomical Clock and Celestial Tracking Program Page 69 Orbital Elements Date: 15-03-1989 M Mean Anomaly: 334.29342 w Argument of Perihelion: 68.76240 Long of Ascending Node: 235.12759 i Inclination: 8.37950 e Eccentricity: 0.21976110 a Semi-Major Axis: 2.33431886 AU B Std Blue Magnitude @ 1AU: 7.23 If a minor planet number was requested, the following prompt will also appear: Press RETURN to ACCEPT, SPACE to cancel: As indicated, press RETURN to accept the minor planet or press SPACE to return to the main Minor Planet Selection menu. If a minor planet name was requested, the following prompt will appear instead: Press RETURN to ACCEPT, SPACE to continue: If this is the desired minor planet, press RETURN to accept it. If you wish ASTROCLK to search further for another match to the requested name, press SPACE. The process will continue until a minor planet is accepted or until the end of the catalog has been reached. Once accepted, the minor planet data is treated in almost the same manner as that for a major planet. The positional data will be automatically displayed, unless Display Mode 0 was selected (degree symbol omitted): VICTORIA Positional Data [J1989.1] [Osculating elements as of 1989 MAR 15] Heliocentric Longitude: 252 37'40.34" Heliocentric Latitude: 2 32'11.13" Heliocentric Radius (AU): 1.9520963 Appar Geocentric Longitude: 275 40'38.95" Appar Geocentric Latitude: 2 02'35.38" Geocentric Distance (AU): 2.4224614 Apparent Right Ascen [J1989.1]: 18:24:21.39 Apparent Declination [J1989.1]: -21 16'48.43" Apparent Right Ascen [J2000.0]: 18:25:00.46 Apparent Declination [J2000.0]: -21 16'25.01" Blue Photographic Magnitude [B]: 10.65 Pressing "9" will display the orbital data. (NOTE: The pi and omega symbols associated with Longitude of the Perihelion and Longitude of the Ascending Node, as well as the degree symbol, have been omitted from this text but appear on the display.) VICTORIA Orbital Data [J1989.1] [Osculating elements as of 1989 MAR 15] M Mean Anomaly: 326 33'52.52" L Mean Longitude: 271 00'02.48" n Mean Daily Motion in Long: 0 16'34.86" ASTROCLK Astronomical Clock and Celestial Tracking Program Page 70 Longitude of Perihelion: 304 26'09.94" w Argument of Perihelion: 68 43'54.29" e Eccentricity: 0.21976110 i Inclination: 8 22'37.22" Longitude of Ascending Node: 235 42'15.65" a Semi-Major Axis (AU): 2.33431886 q Perihelion Distance (AU): 1.82132638 T Perihelion Date: 1985 NOV 21.338043 [B = 7.23] Pressing "0" will select the Tracking Display, as usual, and the data for the minor planet will have been automatically transferred as with the major planets. The tracking data display corresponding to the minor planet VICTORIA indicates the usual data with the prefix "MP #nn", where "nn" is the Minor Planet Number as read from the Minor Planet Catalog. A parenthetical reminder that the data originated with the Minor Planet Catalog is included. The following sample illustrates the data presented: MP #12 - VICTORIA (MP Catalog) EQUATORIAL COORDINATES [J2000.0]: RIGHT ASCENSION (hours): 18:25:00.46 DECLINATION (degrees): -21 16'24.98" HOUR ANGLE (hours): 7:55:04.82 APPARENT COORDINATES [J1989.1]: RIGHT ASCENSION (hours): 18:24:21.39 DECLINATION (degrees): -21 16'48.43" HOUR ANGLE (hours): 7:55:43.90 OBSERVER HORIZON COORDINATES: ALTITUDE [Hc] (degrees): -35 21'31.90" AZIMUTH [Zn] (degrees): 269 30'45.70" Apparent ALTITUDE (degrees): -35 21'31.90" [Charts SA=22 U=II-339] [BMag = 10.65] Entering Orbital Parameters You may also enter the orbital parameters for an orbiting body directly. The orbital parameters are the same as those used for the minor planets. In this case, use the "Z" selection on the planet selection menu. The following data are required: Object Name Ecliptic Epoch Elements Date (D,M,Y) M Mean Anomaly w Argument of Perihelion Long of Ascending Node i Inclination e Eccentricity a Semi-Major Axis B Std Blue Mag @ 1AU In order to determine an elliptical orbit, six orbital ASTROCLK Astronomical Clock and Celestial Tracking Program Page 71 parameters are required, often referred to as "osculating elements". To these are added the ecliptic date of the data (to determine the coordinate system used) and the date of the parameters. Since this function is patterned after the minor planet function, the standard blue photographic magnitude measured at one Astronomical Unit is also requested. Each item shown in the list above will be requested in turn. The Object Name may be entered in upper or lower case letters but will be converted to all upper case letters by ASTROCLK. For most minor planets and similar bodies, the Ecliptic Epoch is B1950; enter the epoch as either Besselian or Julian, designated by the letter prefix "B" or "J" (upper or lower case) respectively, followed by the full epoch year and optional decimal fraction (e.g. B1950.0). The Elements Date is the date for which the orbital parameters are accurate; enter as day-month-year or by any of the other date formats used with Function Key F3; regardless of the input format used (calendar date, julian date, epoch, etc.), ASTROCLK will convert the information to standard calendar date. The position of an orbiting body may generally be calculated for dates within a few months of the date of the orbital parameters and still retain reasonable accuracy. Once all of the orbital parameters and other data have been entered, they will be displayed again, as interpreted by ASTROCLK, along with the following message: Press RETURN to ACCEPT, SPACE to cancel: If the data are correct, press RETURN; if not, press the SPACE BAR and the data will be discarded. Operation from this point is identical with normal minor planet selection above.