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SkyMap Version 2.10 Introduction ------------ SKYMAP is a menu-driven, high-precision celestial mapping program for gener- ating star fields on an EGA/VGA monitor and/or an HP Laser Plotter (or any similar hardcopy device that accepts the Hewlett Packard Graphics Language). Polar, rectangular and alt-azimuth map projections are supported, which can be plotted at any scale and centered on any coordinate. Stars can be plotted for any epoch, with defaults for Besselian 1950.0 (B1950) and Julian 2000.0 (J2000). Proper motion, precession, nutation, parallax and atmospheric refraction effects are all included. In addition to stars, SKYMAP also plots the sun, moon and planets using the equations of Jean Meeus to full precision. The positional accuracy of the moon is roughly 10 arcseconds, while the sun's is better than 5 arcseconds. With the exception of Pluto, planetary locations are accurate to around 10 arcseconds. Pluto's positional accuracy is not known, but is better than 30 arcseconds between the years 1885 and 2099. On the screen, the planets are colored-coded as follows: Mercury-dull red, Venus-cyan, Mars-bright red, Jupiter-bright purple, Saturn-yellow, Uranus- green, Neptune-blue, and Pluto-dark purple. (Color-coding is used for the screen because labeling would be awkward and positionally inaccurate). On the hardcopy, the planets are plotted as unfilled circles (to distinguish them from the stars which are filled), and the user has the option of labeling them with a single letter (m,V,M,J,S,U,N,P) or their full names. Although SKYMAP can be used simply to plot near-publication-quality celes- tial maps, it's greatest feature is its ability to superimpose a time- tagged satellite trajectory. Using a standard NASA 2-line element set, SKYMAP can plot the trajectory of any low-earth orbit (LEO) satellite against the stars as it would be seen from any location on earth. (SKYMAP uses Space Command's SGP, SGP4 and HANDE algorithms, which are designed to propagate the element sets of satellites with periods under 225 minutes. Since nearly all satellites that are visible to the unaided eye fall into this category, the SDP4 deep-space routine has not been implemented. SGP, SGP4 and HANDE will still make predictions for "deep-space" satellites, but with somewhat decreased precision.) Similar to the way it handles satellites, SKYMAP also supports trajectory plotting of rocket boosters. In this case, the 2-line ephemeris file is replaced by a rocket trajectory file that contains a tabular listing of a rocket's position as a function of time. The format for each line of the trajectory file is: mission elapsed time (MET) in seconds, geodetic lati- tude in degrees, longitude in degrees, and altitude in kilometers. Negative values are entered for south latitudes and west longitudes. The MET values need not be at regular intervals, but they must always increase. SKYMAP will linearly interpolate the rocket's position for times occurring between two tabular entries. Obtaining Satellite Ephemerides ------------------------------- To achieve maximum satellite prediction accuracy, your ephemerides should be as current as possible. NASA two-line element sets can be found on the Rancho Palos Verdes Bulletin Board System (RPV BBS), (310) 541-7299, oper- ated by Dave Ransom. These files are located in file area #4, are of the form NASAxxx.TXT, and are updated approximately twice weekly in the PAK compression format. SKYMAP is also compatible with elements provided by Ted Molczan on the Canadian Space Society bulletin board. These elements are updated less often, but also appear in compressed format in file area #4 of the RPV BBS. Their file names are of the form N2L-XXX.PAK. Sun, Moon, and Planet Sizes --------------------------- The sun and moon are plotted at their true angular sizes, except when the field of view of the map is large. The sun and moon are always plotted at least 20% larger than Sirius, so that the full moon (which is plotted white) can be distinguished from the stars, and the sun (plotted yellow) can be distinguished from Saturn. Otherwise, if a map was plotted with, say, a 120-degree field of view, the sun and moon would appear as pinpoints. Keep this fact in mind when studying how a solar eclipse or planetary transit will look; if the map scale is too small (i.e. large FOV) then the sun and moon will appear larger than actual size. This could lead to the false impression that an eclipse or transit is occurring, when perhaps the bodies are just close to one another. To verify that the sun and moon are being plotted at ACTUAL size, decrease the field of view of the plot and see if they appear larger--if so, you are seeing them at actual size. The tran- sition point is somewhere around a 15-degree field of view. At the present time, SKYMAP does not plot the planets at their actual angular size, but this option will be added in a later version. Differential Refraction ----------------------- As of version 2.10, the effect of differential refraction on the appearance of the sun and moon is modeled in SKYMAP. This apparent "flattening" of the sun and moon near the horizon occurs because the upper portion of the image has not been refracted by as much as the lower portion, thus compressing the image vertically. SKYMAP includes differential refraction (in the alt-azimuth projection only) for the sun and/or moon when their centers are less than five degrees above the horizion. Video vs. Hardcopy ------------------ Due to the limited resolution of monitors, much of the labeling that appears in the hardcopy cannot be sent to the video. For example, right ascension and declination grid labels, and satellite/rocket date and time tags appear in the hardcopy only. Also, SKYMAP does not (by itself) create hardcopy output; instead, it generates an HP-GL (Hewlett Packard Graphics Language) file which is compatible with HP plotters such as the HP7475A. With a ras- terizing program such as PRINTGL or Print-A-Plot, HP-GL files can be output on an HP LaserJet II or similar printer. (PRINTGL can be found on Dave Ransom's RPV BBS). Due to the large size of the HP-GL files that SKYMAP can produce (particularly for maps plotted to magnitude 8.1), your laser printer must have at least a megabyte of add-on memory to support plots at the full 300-dpi resolution. If your laser printer has insufficient memory, you will have to reduce the resolution to 150- or possibly 75-dpi in the rasterization program for the file to be printed successfully. Star Data Files --------------- SKYMAP's star data files are based on the Smithsonian Astrophysical Obser- vatory Star Catalogue (SAO), epoch B1950. The SAO contains some 259,000 stars, but only those stars with visual magnitude brighter than 8.1 are presently used by SKYMAP. This 51,000+ star subset was first converted from a 150-byte ASCII format to a 49-byte binary format for use with SKYMAP 1.2 and other astronomical software. Later, the 49-byte format was further condensed to a 28-byte per star format. While the 49-byte format retains all the information present in the original 150-byte ASCII source, the 28- byte format contains only the right ascension, declination, visual magni- tude and proper motion for each star. Earlier versions of SKYMAP accepted both the 28-byte and 49-byte star file formats. However, since run times are cut by as much as 30 percent using the 28-byte format, over a megabyte of disk space is saved, and modem transmission time is reduced by 43 percent, SKYMAP no longer accepts the 49-byte format (as of version 2.5). The 28-byte SAO catalogue can be found in file area #6 of the RPV BBS. This catalogue is stored in 22 separate files, STARS01.DAT through STARS22.DAT, and has been compressed into 6 archive files, SMSTARS1.PAK through SMSTARS6.PAK. Once downloaded and unPAKed, you should have 22 files each containing 2350 stars, with the exception of the last which has 1773. Prior to version 2.5, SKYMAP would run using these 22 files with no further modification. However, in an effort to "clean up" disk directories, SKYMAP now uses a SINGLE star datafile. A program called BIGSTAR is provided in file area #6 to concatenate the 22 files into a single star file. This program also gives you the option of filtering the catalogue to a desired visual magnitude limit. This way, if you are only interested in stars through 6th magnitude, you don't have to carry the overhead of all 51123 stars (90% of which are dimmer than 6th magnitude). A second program called P2000 is available in file area #6 to precess and proper motion the SAO catalogue from B1950 to J2000. SKYMAP will perform precession and proper motion itself, but if you find that the majority of the time you will want maps plotted for J2000.0, you should run P2000. This way, YOUR map epoch matches the star catalogue epoch, so that preces- sion and proper motion are unnecessary when running SKYMAP. This, of course, accelerates the rate at which stars are plotted. The precession and proper motion transformation does present a problem. Prior to transformation the catalogue is sorted by right ascension, but not so afterward. Precession to J2000 increases the right ascension of all stars, which means that some stars which appeared toward the end of the B1950 SAO catalogue will appear at the beginning of the J2000 catalogue. Furthermore, proper motion scrambles the order of the stars. In order to make use of a time-saving indexing scheme, SKYMAP expects its star file to be in increasing order of right ascension. For this reason a third program called SORTSTAR is provided in file area #6. This program uses a quicksort algorithm, and can rapidly sort a file of up to 52000 stars. For those users who don't need all the stars to magnitude 8.1, but would prefer not to be bothered with running BIGSTAR, P2000 and SORTSTAR, I have generated two ready-to-go files for your use. MAG6.DAT contains all the SAO stars through visual magnitude 6.0, precessed and proper motioned to J2000.0, and sorted by right ascension. This file contains all the stars you are likely to see with the unaided eye. For those with truly dark skies, you may want to go to MAG65.DAT, which has all stars through visual magnitude 6.5. MAG6.DAT has 5093 stars, whereas MAG65.DAT has 9026. Required Files -------------- To run SKY210.EXE, you will need several auxiliary files in addition to the star catalogue and satellite ephemeris/rocket trajectory files. Most important is the configuration file, SKYMAP.CFG, which is discussed below. SATNAMES.DAT is needed if you plan to use SKYMAP to plot satellite trajec- tories. ASTROCLK.CTY (or any city file that uses the ASTROCLK.CTY format) is required if you plan to plot satellite or rocket tracks. Finally, if you wish to label bright stars on the hardcopy with their common names, you will need the file STARNAME.TXT. So, to use all of SKYMAP's capabilities you should have 7 files (not including this .DOC file): SKY210.EXE, a star catalogue file (e.g. MAG6.DAT), SKYMAP.CFG, ASTROCLK.CTY, SATNAMES.DAT, NASAxxx.TXT or XXX.N2L, and STARNAME.TXT. Configuration File ------------------ There are 23 lines in the configuration file SKYMAP.CFG. Using a text editor, these lines can be modified to represent your particular location and operating mode. Alternatively, SKYMAP gives you the option of changing the values in the configuration file at run-time, which is probably easier and safer. The configuration file format is as follows: Line 1: Name of star data file (e.g. MAG6.DAT) Line 2: Epoch of the star catalogue (e.g. J2000) Line 3: Julian date of star catalogue epoch Line 4: Name of 2-line elements or rocket trajectory file (e.g. NASA909.TXT) Line 5: Name of city file (e.g. ASTROCLK.CTY) Line 6: Name of your city or viewing site Line 7: Longitude, latitude, altitude, and zone hour of site Line 8: 6 special codes for program mode, local/UTC toggles, lighting constraints and star/planet labeling mode Line 9: Month, day, year, hour, minute, second, track duration, track resolution, timetag resolution, SGP model type Line 10: Code for projection type, right ascension of plot center, declination of plot center, azimuth of plot center, elevation of plot center, right ascension grid spacing, declination grid spacing, rectangular plot field of view, polar plot field of view, alt-azimuth plot field of view, and dimmest visual magnitude to plot. Line 11: Julian date of map epoch, ASCII map epoch (e.g. 9/25/91) Lines 12-21: Names of up to 10 satellites to be overplotted Line 22: Title of plot Line 23: Name of plot file (default SKYMAP.PLT) On line 7, longitude must be from -180 to 180 and latitude from -90 to 90 degrees. Altitude is in meters, and the zone hour is the time difference from GMT. Zone hour must be an integer from -12 to 12. For the west coast, the zone hour is -8 for Standard Time and -7 for Daylight Savings Time. If you decide to use a text editor to modify the contents of SKYMAP.CFG, and accidentally corrupt the file, DON'T PANIC. Just delete it, and run SKYMAP. When no configuration file is present, SKYMAP will create a default SKYMAP.CFG which you can use as a starting point. The City File ------------- The city file can have any name, and although it won't be referenced unless you plot a satellite or rocket track, the file still needs to "exist". If you plan to use SKYMAP to plot celestial maps only, just create an empty file for SKYMAP to find and ignore! (The same applies to the ephemeris file -- in fact, you could create a file called NUL.DAT, and use this name on lines 4 and 5 of SKYMAP.CFG). Running SKYMAP -------------- Type SKY210 from your DOS prompt. If you've prepared everything properly, something similar to the following messages will appear on your screen: Reading configuration information from SKYMAP.CFG Total # of stars in MAG65.DAT: 9026 Configuration information load successful. Hit any key to begin If SKYMAP.CFG is missing, you will instead see the following: Warning: SKYMAP.CFG not found in current directory. Creating default configuration file. Reading configuration information from SKYMAP.CFG Total # of stars in MAG65.DAT: 9026 Configuration information load successful. Hit any key to begin There is quite a bit of error checking during the configuration load se- quence, with automatic recover procedures when at all possible. In the case of a missing star data file, you will get a message like the following: Star datafile "MAG65.DAT" not found. Enter new star datafile name, or return to quit: This allows you to use a star data file with a name different from that which appears in SKYMAP.CFG. As you would expect, some errors are not recoverable. For example, if SKYMAP.CFG happened to be missing lines 11 through 23, you would see the following message: FATAL ERROR. Unexpected EOF reading line 11 of SKYMAP.CFG. Delete SKYMAP.CFG and re-run to create default configuration. As mentioned before, if you can't get SKYMAP to run with your particular configuration file, and you can't locate the problem, delete SKYMAP.CFG and run SKY210. SKYMAP will always create an acceptable configuration file if SKYMAP.CFG is missing. SKYMAP Menus ------------ SKYMAP is menu driven, which makes program operation very easy, even for the beginner. Once you get the message, "Hit any key to begin" following a successful configuration load, you're all set to go. Hit a key: the screen will clear to a blue background, and SKYMAP's main menu will appear: SKYMAP MAIN MENU F1 Star catalogue information F2 Observer site information F3 Change date/time F4 Map attributes F5 Plot mode: Star Map Only F6 HPGL output filename: SKYMAP.PLT [F7 Satellite/rocket information] [F8 Set lighting constraints] F9 Display sun/moon/planet coordinates F10 Plot star map ESC Exit (Commands F7 and F8 only appear when the plot mode listed for F5 is either 'Satellite Trajectory' or 'Rocket Trajectory'.) Use your keyboard function keys or the escape key to select the appropriate menu item. (Striking other keys just results in "beeps".) In addition to SKYMAP's Main Menu, there are six submenus: Star Catalogue Menu (F1), Observer Site Information Menu (F2), Date/Time Menu (F3), Map Attributes Menu (F4), Satellite/Rocket Information Menu (F7), and Lighting Constraint Menu (F8). Use the Escape key to return to the Main Menu from any of the submenus. General Operation ----------------- As most of the menus are self-explanatory, I will make only passing remarks on most of the features, and concentrate on the less obvious ones. You will probably only have to call the Star Catalogue Menu (F1) once for your particular setup. Here you select the star catalogue file you wish to use (e.g. MAG6.DAT) and the magnitude of the dimmest star to be plotted on your map. Be sure to set the star catalogue epoch (F2) to match the epoch of the catalogue (B1950, J2000, etc.). For MAG6.DAT and MAG65.DAT this should be J2000. Go into the Observer Site Information Menu (F2) if you wish to display and/or modify your current site. To change ground sites, hit F2 and then enter the name of the desired location. SKYMAP will search your city file to locate the coordinates of your site. Note that you do not have to enter the entire city name, just enough to identify it. SKYMAP searches for matches, and with each match asks if it has found the city you want. If not, it continues searching until it has read the entire city file. If your city is not found, you will have to enter its latitude, longitude, altitude and timezone yourself. Remember that south latitudes and west longitudes are entered as negative numbers, and altitude is in meters. The timezone must be from -12 to 12 (e.g. -8 for California during standard time). Once you've entered a site's coordinates, you have the option of adding it to the city file using function F5. There are also functions for changing the altitude and timezone of an existing site. This is helpful when switching between Standard Time and Daylight Savings Time. Date/Time Menu (Main Menu-F3) ----------------------------- Use this menu to change the date, time, time type (local or UTC) and DeltaT. The time type is a toggle -- each time you hit F4, it changes between local and UTC. Note that the Date/Time and Julian Date are inter- related. If you change the Julian Date, the starting date and time change accordingly, and vice versa. Also, each time you use F1, F2, or F3, Delta T is recalculated. (Delta T is the difference between UTC and Ephemeris Time, ET). If you want to use a particular Delta T, set the date and time first, THEN set Delta T using F5. Map Attributes Menu (Main Menu-F4) ---------------------------------- This is the menu you will be using most. Here you control how the plot will appear. Function F1 toggles the map type between Rectangular, Polar and Alt-Azimuth. The rectangular projection is appropriate when plotting portions of the celestial sphere that are within 40 degrees of the equator; otherwise, a polar projection should be used as this will minimize distor- tion. The Alt-Azimuth projection is probably what you'll use the most since this shows you how YOUR sky will appear. With the alt-azimuth pro- jection you control the azimuth and elevation of the center of your plot, and the vertical field of view. Azimuth is measured in degrees clockwise from north; thus, east is 90, south is 180, west is 270 and north is 0. Elevation is measured from 0 to 90, 0 representing the horizon, and 90 the zenith. As an example, if you want a view to the south-west that includes the horizon and the zenith, you would set the azimuth to 225, the elevation to 45, and the vertical field of view to 90. Grid spacing (F3) controls the frequency of overlaid grid lines in right ascension and declination for rectangular and polar plots, and azimuth and elevation in the alt-azimuth plot. Values of 10 or 15 degrees are good for large fields of view. I like to have between four and eight grid lines in each direction, so I choose a round number grid spacing (1, 2, 5 or 10 degrees, typically) that is four to eight times smaller than my field of view. If you want no grid at all, enter zeroes or negative values for the grid spacing. On the screen the grid appears cyan. For the alt-azimuth map projection, a green local horizon line is also plotted. (For sites at sea-level, the horizon coincides with the zero-degree elevation line). F4 is used to change the field of view of the plot. For the rectangular projection, you select the horizontal (right ascension) field of view in hours; for the polar and alt-azimuth projections you set the vertical field of view in degrees. The epoch of your plotted map can be changed using F5. Most of the time you will want this epoch to match that of your star catalogue, usually J2000 or B1950. However, you can plot the map for any epoch -- it just takes a little longer due to precession, nutation and proper motion calcu- lations. If significant precession must be performed, the map can take quite a bit longer to plot, especially if the star catalogue is large (more than 10000 stars). This is because the internal star file indexing scheme can no longer be used, which requires the entire star file to be read. For small fields of view, this means a lot of time is spent processing stars that will not appear on the plot. F6 allows you to enter a title for your hardcopy SKYMAP output. The title can be up to 70 characters and will appear left-justified below your map. If you don't want a title, enter F6 and hit return. F7 is a three-way toggle controlling how planets and stars are labeled in your plot. The default is no star labeling, and a single-letter planet label (m,V,M,J,S,U,N,P). Hit F7 once, and single-letter planet labels change to full names. Hit F7 again, and bright stars are also labeled with their common names (e.g. Polaris, Betelgeuse, Rigel, etc.), provided that STARNAME.TXT is found in your directory. (This file contains common names for 195 stars). Hit F7 a third time, and you're back to the default. Prior to version 2.10, the star/planet labeling status was not stored in SKYMAP's configuration file, but this information has been added to line 8. This improvement unfortunately comes at the expense of upward compatibility: a V2.9 or earlier .CFG file will not run properly with V2.10 unless an extra 0, 1 or 2 is added at the end of line 8 of the file. Plot Mode (Main Menu-F5) ------------------------ Function key F5 in the Main Menu is a plot mode toggle. There are three modes: Star Map Only, Satellite Trajectory and Rocket Trajectory. Very few of you will ever use the Rocket Trajectory mode, so I will not discuss it here except to say that this mode can be used to plot the track of a rocket (or any object for that matter) as it would be seen against the stars from your particular viewpoint. A rocket trajectory file is required for this mode, and its format was described in the introduction. The Star Map Only mode can be used if you don't want to overplot a satel- lite trajectory. In this mode, Main Menu functions F7 and F8 will not appear. HPGL Output Filename (Main Menu-F6) ----------------------------------- A word on the plot file. SKYMAP *always* produces a plot file, whether you want it or not. (This is an artifact of the program's evolution from the days when screen output was not yet implemented). You can always delete the file later if you don't need it, so just give it any name. The program will check to see if the file already exists, and if so, give you the option of writing over it or selecting another filename. Plotting a Satellite Trajectory ------------------------------- Plotting a satellite trajectory used to require a bit of preparatory work BEFORE running SKYMAP, as SKYMAP did not have the "brains" to know when a particular satellite was going to make a favorable pass over a given site. A user had to first run a program such as Paul Traufler's TRAKSAT or Dave Ransom's STSORBIT to know when and where a good pass would occur. As of version 2.9, SKYMAP will now do this for you. An analytical search func- tion has been added to the Satellite/Rocket Information Menu under F8. You provide the search duration (in days) and the minimum elevation that the satellite must exceed. This search is subject to any lighting constraints you have set. (Lighting constraints are discussed later). If you have loaded multiple satellites, you must also provide the index number (1-10) of the satellite to search on. While the search is proceeding, a date counter will appear to advise you of progress. You can abort a search at any time by hitting the escape key. If no acceptable passes are found within the search duration, a message to that effect will appear for a few seconds, and then control will return to the satellite menu. If a pass is found, the starting date and time of the pass will be displayed along with the peak elevation. (This starting date and time will be three minutes before the satellite breaks your horizon). SKYMAP will automatically center your viewpoint on the peak of the pass, change your start date and time, and set your search duration to correspond to the pass. If your plot mode was rectangular or polar, it will be changed to alt-azimuth. The search function has been tested with a many satellites from different viewing locations, and seems to work well; however, the logic flow is very tricky due to interaction with the lighting constraints, and it is possible that the algorithm will have problems in particular situations. If you run across such a case, and your problem is repeatable, please let me know so that I can work on a solution. Satellite Information Menu (Main Menu-F7) ----------------------------------------- With the exception of the lighting constraints (which are set in the Lighting Constraints Menu) and the propagation start date and time (which are set in the Date/Time Menu), all of the Satellite parameters are set in the Satellite Information Menu. F1 allows you to change the name of the satellite ephemeris file, usually of the type NASAxxx.TXT. As mentioned before, Ted Molczan's N2L-XXX format is also accepted by SKYMAP. F3 controls the duration of the satellite propagation, which tells SKYMAP how far into the future to extend the orbital track. For a single pass at a location, a half-hour to an hour is sufficient. If you propagate too far into the future, you may end up plotting multiple passes unintentionally. Remember that the propagation duration in used in conjunction with the start time that you've set in the Date/Time Menu. For this reason, I usually select a start time around 5-10 minutes before the satellite will appear above my site horizon to ensure that none of the track is missing on my star map. Of course, if you use the autolocate function (F8), all of these values will be set for you. The resolution of the trajectory plot (F4) tells SKYMAP how frequently to calculate the satellite's position. The shorter the time resolution, the longer it takes SKYMAP to run, but the smoother the track will look. Tracks are fairly linear over 10-second periods, but if you are plotting a very small portion of the sky you will want even more frequent positional information. When selecting the resolution, you should also be thinking about how frequently you'll want the orbit time-tagged (set with F6). Time-tags must occur at some integer multiple of the trajectory resolution. (Note that time-tags CAN occur at every trajectory point if desired). As an example, if a satellite is going to take 30 seconds to cross your map, I would select a resolution of 1 second, and a timetag resolution of either 1 or 2 seconds. Be careful not to select so short a time between tags that they begin to overlap one another. With a little practice, you'll get a feel for these time-related inputs. F5 is a toggle between UTC and Local Time-tag labels. This is independent of the time type you've established in the Date/Time Menu. For example, your start date/time may be Pacific Daylight Time, but your time-tags can be UTC if desired. Propagation Model ----------------- F7 is a toggle directing which propagation model to use, either SGP, SGP4 or HANDE. Results will vary slightly depending on which model you use, but should agree quite well with each other within a week of a satellite's ephemeris epoch. SGP is the lowest fidelity model, and consequently runs the fastest. SGP4 should theoretically give more accurate predictions, but it takes slightly longer to run. There will be negligible cross-track dif- ference between SGP and SGP4, but the along-track position may differ by several seconds depending on how "fresh" the orbital elements are. The HANDE algorithm is the most sophisticated. It was developed by Felix R. Hoots for Air Force Space Command, Colorado Springs, Colorado, and first appeared in Spacetrack Report #6 - Models for Propagation of Space Command Element Sets, in July of 1986. At that time, it was projected that in the early 1990s all Space Command element sets would be generated with the HANDE model, and that the element sets sent to external users would be pure HANDE elements (in contrast to the current method of sending a mixture of Brouwer and Kozai elements). However, the last time I checked with Space Command there was no near-term plan to make the switch. I've included the HANDE model in SKYMAP for the curious, and I would be interested in hearing how it stacks up against SGP4 in terms of prediction accuracy. For great- est accuracy, HANDE needs special 17-element (3-line) ephemerides, but it will run with 2-line elements, albeit with degraded accuracy. Satellite Selection ------------------- Satellites are selected using function F2 in the Satellite Information Menu. This function allows you to add, change or delete entries from a list of up to ten satellite names. To delete a satellite from the list, enter F2 and hit "D" followed by a return. Then input the list number (1-10) of the satellite to be deleted. To add a satellite, enter F2 and then hit "A" followed by a return. SKYMAP will then ask you to enter either a five-digit NORAD designation (e.g. 16609 for Mir), or a satellite name. Numbers have an advantage over names in that they are unambiguous, but names are easier to remember. Selecting satellites by name is similar to searching for a city name in the city file. To find a particular satellite, SKYMAP does not need the whole name; just enough of it to distinguish it from other satellites. As an example, entering just "Mir" for the satellite name is not sufficient to distinguish the Mir Space Station from the Miranda satellites. Entering "Mir s" clears up the ambiguity. When SKYMAP finds a match, it displays the full name of the satellite it has has found, and gives you the option of accepting it, or continuing to search for further matches. If no acceptable matches are found, SKYMAP will report "Name string not found.", and ask you to enter another name or number. To change a satellite in the list, hit F2 followed by "C" and return. Input the list number (1-10) of the satellite to be changed, and follow the normal instructions for adding a satellite. As of version 2.10, control stays within the satellite list editor until 'E' is entered (for end), or any key other than A, C or D is entered. (This change was made to facilitate multiple changes to the satellite list.) SATNAMES.DAT file ----------------- The file SATNAMES.DAT is used to connect satellite names with their NORAD numbers. Since new satellites are continually being launched, you may want to occasionally add entries to this file. As with the city file and configuration file, this can be accomplished with any text editor. Just follow the format of the other entries in the file, and keep the NORAD numbers in increasing order. The first six characters of each line of the file must be the 5-digit NORAD designator followed by a space. The next four characters are the satellite's standard visual magnitude, which is described below. The name you want to use to identify the satellite begins in column 11. Feel free to use any name you like, and to modify any of the names already in the file. (You can also delete file entries for satellites that don't interest you). You'll notice that for satellites which don't yet have a name, I've used the NORAD number and letter scheme. Standard Visual Magnitude ------------------------- The standard visual magnitude appears in columns 7-10, and is meant to represent the approximate visual magnitude of the satellite if it were at a range of 1000 km and a phase angle of 90 degrees (half-illuminated). My VIEWSAT program uses this value to predict the visual magnitude of a satellite as a function of its actual range and phase angle, but SKYMAP makes no such calculation at the present time. It is included only for compatibility reasons, but I've mentioned it here for the curious. Most of the standard magnitude values in SATNAMES.DAT come from the N2L-xxx type element sets, courtesy of Ted Molczan. In general, I've found these values to be slightly pessimistic, and in a few cases I've made changes to reflect observations that I've made. Entries of "99.9" are used for satellites which appear in the NASA bulletins, but not in Ted's N2L-type files. Ted's two-line element sets concentrate on satellites which CAN be visible to the unaided eye, so those satellites with standard magnitude entries of 99.9 are either too dim for unaided viewing or too recently launched for a measurement to have been made. Lighting Constraints Menu (Main Menu-F8) ---------------------------------------- Lighting constraints control what portions of an orbital track are plotted. Functions F1 through F3 control toggles on the three different lighting constraints: sun at the satellite (F1), sun at the ground site (F2), and moon at the satellite (F3). For sun and moon at the satellite, F1 and F3, the three possible conditions are Visible, Eclipsed, and No Constraint (i.e. don't care). As of version 2.10, there are five possible lighting conditions at the ground site: Day Only, Night Only, Sunset to Midnight, Midnight to Sunrise, and No Constraint. How these lighting constraints are set will determine which satellite passes the autolocate function (F8 in the Satellite Information Menu) will accept. For example, if you don't like to get up for those early morning satellite passes, hit F2 until the line reads "Sun at ground site: Sunset to Midnight". Display Sun/Moon/Planet Coordinates (Main Menu-F9) -------------------------------------------------- This function was originally added for debugging purposes, but I found it useful enough that I decided to add it as a feature. If you want a tabular display of the TOPOCENTRIC sun, moon and planet coordinates for your selected site, date and time, just hit F9. Note that through clever selection of your site, you can display GEOCENTRIC coordinates instead. In the Observer Site Information Menu, select a site name that you know won't be found in your City File (say "ZZZ"). When the unsuccessful search of your City File is complete, SKYMAP will ask for the site coordinates. Just enter a latitude of zero, any longitude, and an altitude of -6378135 (the equatorial radius of the earth in meters). Your site is now the earth's center! Plot Star Map (Main Menu-F10) ----------------------------- Once you've input all the necessary parameters and you're ready to plot, hit F10. If any satellite information needs to be loaded, brief messages may appear at this time. Then the screen will clear, the sun, moon and planets will be plotted (if they are visible), followed by the stars. The stars may take a while, particular in the alt-azimuth projection which has to read your entire star file. Finally, a cyan grid will be plotted (if it was selected), and any satellite tracks will be overplotted in bright red. (While each satellite's track is being plotted, its name, NORAD designation, perigee, apogee and period will appear above the plot, along with a percent completed indication.) When the plot is complete, the message "Hit any key to clear screen and goto Main Menu" will appear in green below the map. Exiting SKYMAP (Main Menu-ESC) ------------------------------ Use the escape key in SKYMAP's Main Menu to exit the program. The program will then ask whether to save current configuration parameters. The default is no, and if you hit return SKYMAP.CFG will remain unchanged. If you made configuration changes that you want to save, enter 'Y'. That's it! You're done! Your SKYMAP HP-GL file is ready to be plotted (or rasterized and printed). Problems -------- The SKYMAP source code is over 9300 lines long, and as with anything of this size, bugs can pop up. If you experience a problem that seems to be repeatable and can describe it clearly, please leave me a message on the RPV BBS. Sometimes it's just a user mistake. For example, if a satellite track isn't appearing that you know should be, check the search duration, lighting constraints, the zone hour of your site, the time-type of your time and date (UTC or local), and make sure you're looking in the right part of the sky. Bugs have been found by SKYMAP users before, and it is likely there are more to be located. Usually bugs crop up when significant features have been added to a new version, and there have been over 2500 lines of code additions/changes in the last two versions alone. New Features ------------ I am always ready to listen to user's suggestions on improvements to SKYMAP. Upcoming features under consideration include the addition of minor planets and galaxies, the option to plot planets at their actual angular size, a toggle to plot constellation line segments, and some added intelligence to accelerate star plotting in the alt-azimuth mode. Revision History ---------------- February 27, 1991 - First major release (1.0). Rectangular and polar plots supported with labeled grids. Satellite trajectories plotted with timetag labels tilted 45 deg w.r.t. track. Proper motion and precession not yet taken into consideration. March 7, 1991 - Precession and proper motion added; date now only entered once; defaults added to lighting constraint questions; option added to keep lighting constraints unchanged for multiple track plots; city name can be entered instead of lat-long-alt (coords are then extracted from Dave Ransom's ASTROCLK.CTY). Rolling orbit track timetag replaced by % completed counter; polar plot labels changed so that all are right side up; B1950 map epoch default added along with selection for J2000; satellite coordinates precessed to match those of star map; epoch of map printed at bottom center of plot. March 9, 1991 - Configuration file added with default file names and location information. March 11, 1991 - Orbital element format switched to NASA two-line format; satellite name or title added below plot; map epoch label moved to the right. March 13, 1991 - Version 1.1 release. Timetag label plotting logic improved so that no label is printed upside-down; south polar plot inverted so that all polar plots have their highest declination at the top of the page; 49-byte star catalogue format now accepted in addition to prior 28-byte format; star record size added to configuration file; if pre- cessing catalogue by more than 50 years, all star files now opened. March 14, 1991 - Error found in precession algorithm: decl could exceed 90 degrees; rewrote vector rotation part of algorithm. March 20, 1991 - Version 1.2 release. Rocket launches can now be plotted against star map; bug fixed in Eclipse subroutine for satellite or rocket altitudes with Rho < 1; DrawSegments no longer used by Tracks subroutine, so tracks are plotted continuously on screen rather than all at once; bug with southern hemisphere polar declination labeling fixed. April 9, 1991 - SKYMAP.CFG created w/ default values if not found; end-of- file check while reading line 6 of configuration file. May 15, 1991 - Version 2.0 release. Menus added; all parameters stored in configuration file; single satellite plot per map. May 21, 1991 - Version 2.1 release. Sun and moon added; time now entered as HH:MM or HH:MM:SS instead of HHMM.SS; alt-az map projection added; moon phase added. June 3, 1991 - Version 2.2 release. Multiple satellite track option returned (up to 10 satellites); satellite tracks labeled with NORAD # to distin- guish them from one another; sun and moon scaling changed to the larger of their actual size and 1.2 x the size Sirius; screen border changed from dull red to bright white; more informative ephemeris loading mes- sage; early EOF error checking on SKYMAP.CFG; dashed halo added to sun to distinguish it from full or new moon on laser plotter; planets added as labeled open circles on hardcopy, filled color circles on screen. June 7, 1991 - Version 2.3 release. Planet precession added; PlotEpoch read bug in GetConfig fixed; star information now read from a single direct- access star file indexed by STARS.IDX; binary star search added; bug with satellite propagation in Alt-Az mode fixed. June 10, 1991 - Discovered and fixed bug that prevented Rocket trajectories from being plotted (caused by multi-satellite upgrade). June 20, 1991 - Version 2.4 release. HANDE algorithm added; variable zoom and center elevation added to Alt-Azimuth projection. June 24, 1991 - limit determination logic added to polar grid plot to speed it up. July 16, 1991 - Version 2.5 release. Limit logic added to Alt-Az grid to speed it up and to correct missing azimuth lines at high magnification; sun and moon routines replaced with Jean Meeus' equations found in Astronomical Formulae for Calculators, Fourth Edition (nutation and aberration now included); DeltaT correction added to convert to ephemeris time. July 31, 1991 - DeltaT automatically calculated (if desired); Astronomy, time and date routines moved to a new module called ASTRO (Module SUN deleted). August 26, 1991 - Version 2.6 release. HPGL file added to configuration file; SKYMAP.CFG made upward compatible thru EOF checking in GetConfig; planetary equations replaced with those which appear in Astronomical Formulae for Calculators, Fourth Edition; mean sidereal time calcula- tion replaced by apparent sidereal time; bug in site altitude discovered and fixed (type mismatch in SetSite); menu site altitude output in meters or kilometers depending on magnitude of altitude; annual aberra- tion and nutation corrections added to stars. September 11, 1991 - Version 2.7 release. Light-travel time added to plane- tary calculations; menu item added to output tabular information on sun, moon and planets; bug in AGrid line-labeling fixed (back to labeling at sides and bottom); planet and bright star name labeling added. September 24, 1991 - Version 2.8 release. DMS routine improved; 49-byte star file format no longer accepted; starfile record size removed from SKYMAP.CFG file (but made upward compatible from V2.7); STARS.IDX no longer used - index values are calculated at load time and whenever the star catalogue is changed. October 7, 1991 - Bug due to improper Solar and Lunar calls in Subroutine Tracks located and fixed; AGrid range bug fixed. October 16, 1991 - Version 2.9 release. Added automatic search for next satellite pass; map center displayed below map (on screen only). November 11, 1991 - Version 2.10 release. Fixed reported number of stars read in (was off by one due to header record 0); added logic to label Pleiades as "Pleiades" unless at high magnification; when editing satellite list, remains there until (E)nd entered; planet/star labeling status now stored in SKYMAP.CFG; morning/evening pass filter added; atmospheric refraction taken into consideration in alt-azimuth plots; true horizon added to Alt-Az plot (old "horizon" was actually 90 degree zenith angle); differential refraction included for sun and moon when they are within 5 degrees of the horizon.