JCSM Shareware Collection 1993 November

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:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: : : : : : Skychart 2.0 : : : : UNREGISTERED VERSION : : : : Instructions : : : : : :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: Welcome to Skychart, a graphics oriented Astronomy program. Skychart realistically depicts the appearances and positions of stars and planets for various user stipulated conditions. Skychart also indicates the pos- itions of hundreds of deep sky objects such as galaxies, planetary neb- ulae, and star clusters. Skychart can also print an ephemeris of the sun and planet positions for any given month. Skychart features dynamic and animated displays. Skychart can be used as a guide for amateur observing or simply as an aid in learning the nighttime sky. System requirements: -------------------- To run Skychart, your system must- 1) Be an IBM PC or clone 2) Have a VGA card and monitor 3) Have at least 640k of DOS memory 4) A hard disk with 3 megabytes of free space Not required but highly recommended are- A) A math coprocessor B) A mouse Menu Operation -------------- Skychart is mostly menu driven. In text modes, (ephemeris for example), a menu item is selected by typing the capitalized letter of the item. Mouse operation is not available in text modes. In graphics modes, menu items normally have a highlighted character. The item may be selected by typing the highlighted character or by clicking on the item with the mouse. If the item has no highlighted character, that item is not available at that time. Mouse and keyboard operations may generally be freely mixed in graphics modes. Main Menu --------- The main menu is displayed at the bottom of the initial screen with the galaxy picture. All program functions are accessed through this menu. The Ephemeris ------------- EPHEMERIS: Type 'E' or click the mouse button over this word to display an ephemeris. This function displays an ephemeris (list of positions) for the sun and 8 planets other than Earth. Output may also be sent to the printer. The display is in one of 3 formats: 1- elongation. Elongation is the angle in degrees between an object and the sun as measured along the ecliptic (path of sun in sky). Positive angles indicate the planet is west of the sun and therefore visible in the morning sky, negative angles indicate east and evenings. 2- longitude. Celestial Longitude is the angle in degrees of an object from the Vernal Equinox (00h00m of right ascension) as measured along the ecliptic. 3- RA/Dec. This is the object's position as measured in right ascension and declination. The actual display format for each object is: HHM sDDM and is interpreted as HH hours M0 minutes right ascension, DD degrees M0 minutes of arc declination, with s being + or minus. For example, 123 -231 corresponds to 12 hours 30 minutes RA and -23 degrees 10 minutes of arc declination. To change between formats, type 'F' while in ephemeris mode. Then enter 1 for elongation, 2 for longitude, or 3 for RA/Dec. Initially, the positions are displayed for every other day, starting with the first day of the current month. To change the interval from 2 days to one day, select 'I' for Interval. Each time Interval is selected, the In- terval toggles between 1 and 2 days. When the interval is 1 day, only the first 15 days of the month are displayed. To see the data for the last part of the month, select Next. Selecting Next again shows the 1st 15 days of the following month. When the interval is 2 days, Next will display the following month. The Previous command works similarly, only backwards in time. If you want to see the data for a date far from what is currently display- ed, select 'D' for Date. You will be prompted to enter a new date in the form mm/dd/yyyy. The day value is necessary, but is ignored- the new data will always start at the 1st day of the selected month and year. The Print command will send the contents of the screen to the printer for later reference. The Star Guide -------------- STAR GUIDE: Type 'G' to enter the Guide mode. In this mode, the objects (initially, only stars are displayed), are projected onto a circular area of the screen. Stars appear on screen as they actually appear in the sky- both in position and brightness (and color for the brightest stars). The circle represents all of the sky that can be seen at the current point in time. Since an observer can only see half of the entire sky at once, (or less if there are obstructions near the horizon), only half of all the stars wil be displayed. The circle itself represents the horizon, and just outside the circle, the compass points of North, South, East & West are displayed. This is a dynamic mode, where objects move from east to west to reflect the Earth spinning on its axis. When objects reach the west horizon, they disappear. New objects will appear on the east horizon. All object positions are updated every few minutes. The update interval can be changed through the Settings menu. Note: the updates can take some time on systems without a math coprocessor. The current date is displayed at upper right. Below it are the current so- lar and sidereal times. Below this are the observer's Lattitude and Long- itude. These values can be changed through the Settings function of the main menu (see below). Displayed in the upper left are the current celestial coordinates of the cursor, which resembles a small red cross in the middle of the screen. The cursor can be moved by moving the mouse or by using the keys of the numer- ric keypad. When using the keypad, '4' moves the cursor left, '2' moves it down, '9' moves it up & right, etc. The cursor moves by 1 pixel each time if "NUM LOCK" is on, and by 10 pixels if it is off. As the cursor moves, the celestial coordinates will change to reflect its new position. Objects within the circular sky area can be identified by "selecting" them. To select an object, position the red cursor over the object and click the left mouse button or press ENTER on the keyboard. "Searching..." appears in the upper left corner of the screen, and will be replaced by the object's name when it is determined. For a star, the 2 line identification format is: line 1- sao # or [nn],[ggg],[ccc],[common name],[aaaaa] line 2- magnitude Sao # is a dim star's sao designation. Brighter stars have the alternate form where nn = star's number in its constellation (Flamsteed designation), ggg = greek alphabet (Bayer) designation, ccc = constellation, and aaaaa = designation of the star's companion, if it has one. Planets are simply identified by their name on line 1. Nebulous objects are identified by a 3 line format: line 1- common name (e.g. Ring Nebula) line 1- catalog number, type(e.g NGC 6720 Planetary Nebula) line 2- Messier number magnitude(e.g. M-57 8.8) Catalog number is usually from the New General Catalog (NGC). Types are galaxies, clusters, or nebulae, etc. Messier number is like M-31 for the Andromeda galaxy, and magnitude is total apparent magnitude of the object when available. If more than one object is beneath the cursor, the menu at the bottom of the screen is replaced by the Multiple Objects menu. Up to 5 objects may be displayed, one at a time, by cycling through the list by typing 'N' or 'P' for Next or Previous object. Type 'X' to return to the Guide menu. Guide Menu ---------- At the bottom of the screen in Guide Mode is the Guide menu. It offers the following features: Const- Clicking on this or typing 'C' will draw the imaginary lines between stars in the constellations to highlight them. Selecting this item again turns off the lines. All constellation lines are drawn even if the stars they connect are dimmer than the magnitude cutoff limit (see Magnitude) menu item below. Any line that is partially below the horizon, however, will not be shown at all. Draw- This blanks all objects within the horizon circle and redraws them. Use this to redisplay the stars after turning off the display of constel- ation lines or nebulae or names, if some of the stars were erased in the process. Find- Use this command to find a particular object. Since celestial objects often have many different names, Skychart guides you through the name input process. Upon selecting Find, the Find object menu appears with the following items: Constellation, Nebula, Planet and Star. The available procedures for each are described below. Constellation: Select this to find one of the 88 common constellations. You are prompted for the constellation name. Skychart uses a 'running match' algorithm to input the name. As you begin to type the characters of the name, Skychart will display the name of the first constellation matching this spelling. The running match algorithm minimizes the troubles caused by spelling errors. For example, suppose you want to find Canes Venatici or Pegasus. The following diagram shows what you type and what Skychart displays. YOU TYPE SKYCHART DISPLAYS --------------------------------------------------- C Caelum A Caelum N Cancer E Canes Venatici YOU TYPE SKYCHART DISPLAYS --------------------------------------------------- P Pegasus You generally will only need to type one or two letters to get the con- stellation you want. Once the correct constellation is displayed, press <Enter>. To have Skychart search for it, type 'F' or click over Find. Skychart will attempt to find it. If you decide not to search for it at this time, select Cancel. Nebula: Select this to find one of the deep-sky obects such as a galaxy or planetary nebula. To find an object from the Barnard, IC, Messier or NGC catalog, select the appropriate item. In each of these cases you are then prompted for a number, specifying the entry of the object within that catalog. Type <Enter> after the number. Select Other to search for an object which doesn't have a catalog number, or for an object which has a common name. You are prompted to enter its name. Type <Enter> after the name. Once the common name or catalog name and number is displayed, select Find to search for it or Cancel to abort. As an example, suppose you want to find the Ring Nebula. This can be done in any of the following ways. A) select Find, Nebula, NGC and type 6720 <Enter>, select Find. B) select Find, Nebula, M and type 57 <Enter>, select Find. C) select Find, Nebula, Other and type 'Ring Nebula' <Enter>, select Find. Care must be taken when searching for an object with its common name. Al- though case is ignored, the spelling must exactly match the way it is spelled in Skychart. If the spelling is off, the object won't be found. The following table illustrates this. THESE WORK THESE DON'T WORK ----------------------------------------------- RING NEBULA RING Ring Nebula RingNebula Dumbbell Nebula Dumb Bell Nebula Planet: Select this to find the sun, moon, or a planet. A menu with each of these objects appears. Simply type the highlighted letter or click over the desired object, then select Find to search for it. Star: Select this to find a particular star. Stars, like nebulae, can be known by multiple names. Skychart lets you search for a star by its Bayer, Flamsteed, or SAO designation, or by its common name. A Bayer designation consists of a greek name with optional superscript and a con- stellation name(alpha Orion or pi5 Orion, for example). Select Bayer to search for a star with its Bayer designation. You are then prompted to enter its greek letter. Skychart uses the running match algorithm to in- put greek letters. Begin typing the greek name, and Skychart displays the first matching name. When the correct name is displayed, press <Enter>. You are then prompted to enter its constellation, again using the running match algorithm. When the correct constellation name is displayed, press <Enter>. Then select Find to search, or Cancel to abort. Flamsteed designations consist of a number and a constellation name(52 Orion, for example). Select Flamsteed (type 'L', not 'F') to search for a star by this method. You are prompted to enter the Flamsteed number, followed by <Enter>. Then enter the constellation name and <Enter>. Finally, select Find to search or Cancel to abort. Select SAO to search for a star whose SAO number you know. Simply enter the SAO number(usually a 6 digit number) followed by <Enter>. Select Find to search or Cancel to abort. Select Other to search for a star by its common name. Type the common name and press <Enter>. Select Find to search or Cancel to abort. Again, the case of the name is unimportant, but the spelling must exactly match that by which it is known in Skychart. Example- you may search for Rigel in the following ways. A) select Find, Star, Bayer, type b(beta)<Enter>, type or(ion)<Enter>, select Find. B) select Find, Star, fLamsteed, type 19<Enter>, type or(ion)<Enter>, select Find. C) select Find, Star, Other, type rigel<Enter>, select Find. If SKYCHART is successful in locating the coordinates of your object and it is withing view, the mouse cursor will move to its location on the screen and blink several times. The upper left of the screen will then display the ob- ject's name and other data as if it had been selected. If the object's is lo- cated out of view, SKYCHART displays "Out of view at " and gives the coordi- nates for it. If you want to display the portion of the sky which contains the object, you must change your location or time as described below . Finally, if SKYCHART cannot locate your object, try again with any other name or designation the object may have. Location- This feature allows the observer's location on earth to be changed thus affecting the area of the sky that is visible. Any combin- ation of longitude and lattitude is acceptable. When this feature is se- lected, a new menu appears at the screen bottom. The observer's current lattitude is displayed. To lower the lattitude, type '-' or click the left mouse button when the cursor is over the lattitude value (not the word lat- titude). To increase the lattitude value, type '=' or click the right but- ton over the current value. Legal values are between -90 and +90 degrees. To decrease longitude, type ',' or click the left button over the longitude value. To increase longitude, type '.' or click the right button. Legal val- ues are between -180 and +180 degrees. When the desired coordinates have been entered you can select eXit to keep the new values and return to the Guide menu, or select Update to display the new view from these coordinates but still remain in this menu for further experimentation. Selecting Default will return the coordinates to those that are defined in the Settings menu off of the main menu. Magnitude- By default, all stars in the database are displayed when the program is first run. However, only the stars brighter than a limiting mag- nitude may be displayed if desired. Select Magnitude from the Guide menu to change the limiting magnitude. A new menu appears at the bottom. The current limiting magnitude is displayed. Type '-' or click the left button over the current value to decrease the limit (i.e. fewer stars will be displayed). Type '=' or click the right button to increase the limit. Select Update to see the effect of the new limit at any time. Select eXit to return to the Guide menu with the new limit in effect. Use this feature to simulate the amount of light pollution of your area. For urban residants, a limit of 2 or 3 is appropriate. For rural areas, set the limit at the maximum value. Selecting Default returns the value to the maximum. Nebula- Select this feature to toggle on and off the display of the neb- ulous (or deep-sky) object positions. The positions are indicated by a small square for each object. Examples of Nebulae contained in the database are galaxies, emmision and reflection nebulae, planetary nebulae, star clusters, dust lanes, and others. The object may be identified by centering the cursor inside the square and "selecting" the object as mentioned previously. The database contains over 500 such objects. Planets- Select this feature to toggle display of the sun, moon, and planet positions. These objects appear on the screen similarly to how they would appear in the sky. The sun is a large (compared to other objects) yellow disk, the moon is a large white disk, Mercury and Venus are bright white dots, Mars is a bright red dot, Jupiter and Saturn are bright yellow dots, Uranus and Neptune are dim bluish dots, and Pluto is a very dim grey dot. To more easily distinguish planets from stars, turn the planet display on and off rapidly by successively clicking over the Planets menu item or by typing 'P'. The planets will then blink on and off but the stars won't. Planets, but not sun or moon, can also be identified by "selecting" them as discussed above. pRint- You can send the current view to a laser printer. The printer must be compatible with an HP Laserjet IIP, and must be connected to the first parallel port (LPT1) of your computer. Select 'R' to get a hardcopy. The output will contain planets, constellations, or nebulae if they are currently displayed on the screen. Planets are denoted as follows: *=sun, m=mercury, v=venus, a=mars, j=jupiter, s=saturn, u=uranus, n=nepune, p=pluto, and the moon is displayed as a happy face. The upper left of the printout contains a sample star magnitude guide. Printing can take several minutes, es- pecially if constellation lines are enabled. During printing, a progress report is displayed in the upper left corner of the screen. You can type <ESC> at any time to abort the printing process. Printing error messages- two error codes may arise when printing. The first is error 20- Out of Memory. Your printer does not have enough mem- ory to print the current display. The second is error 21- Page Too Com- plex. The page is too complex for the printer to format as the paper moves through. The solution to both errors is the same- reduce the amount of in- formation to be printed. This can be accomplished by reducing the number of stars being displayed through the Magnitude command, zooming in to reduce the number of objects displayed, or disabling constellation lines, nebulae positions, or object names. Constellation and grid lines normally cause the most problems. Show- Select this item to display constellation names, grid lines, nebulae names, star names, or the ecliptic. When the show menu appears, simply click on the item you wish to display. Click the same item again turns off the dis- play of that item. To reduce cluttering, not all names are always shown. More star names are shown at higher values of zoom factor, since the stars are relatively farther apart as the zoom factor increases. For zoom factors less than 4.0, only common star names are shown. When the zoom factor is between 4.0 and 16.0, Bayer designations are also shown. For zoom factors greater than 16.0, Flamsteed designations are included. The zoom factor is fixed at 1.0 in Guide mode. Grid lines indicate values of right ascension and declination. Lines will be displayed at every hour of right ascension and every 10 degrees of declination. The ecliptic simply indicates the path of the sun through the sky. Time- Guide mode is dynamic- the display is updated every few minutes to reveal the apparent motion of the sky from east to west as the Earth rotates beneath it. Therefore, the current display is dependent on the time. It is also dependent on the day of the year. To temporarily change the time or date of the display, select Time from the Guide menu. A new menu appears. To choose an earlier display date, type ',' or click the left button over the current date. The display date is then one day earlier in the year. To increment the date by one day, type '.' or click the right button. To choose an earlier display time, type '-' or click the left button over current time. Type '=' or click the right button to increase the display time. To see the updated positions of the stars, select Update. You can use this feature to see what time of day or what time of year favors the view- ing of a particular object. Select Default to return the date and time to current values. Select eXit to return to the Guide menu. The new date and time values will remain in effect. If the new DISPLAY time or date is different from the actual current time or date, this is indicated by the time or date being displayed in red in the upper right of the screen. eXit- Select eXit to leave Guide mode and return to the Main menu. The Star Map ------------ STAR MAP: In Map mode, the WHOLE sky is projected onto a rectangular re- gion of the screen. This is similar to a projection of the whole Earth on- to a rectangular map in that it does not represent what may actually be seen from any particular location. Its purpose is to show the relative lo- cations of objects in the sky to one another. The format of the display is of declination being represented vertically and right ascension horizon- tally. Declination values are displayed along the right side of the rec- tangle and right ascension is labeled along the rectangle's bottom. In this projection, right ascension values of 0 and 24 are equivalent and therefore although not evident from the display, objects very near the left and right sides of the map are actually located very near each other. A similar re- lationship does NOT hold for objects near the top and bottom, however. At the top center of the screen is the current date, solar, and sidereal time. At top right is the current Zoom setting (zoom = 1.0) explained below. At top left is displayed the coordinates of the current cursor location which is the red cross in the middle of the map. As in Guide mode, objects within the map may be "selected" by positioning the cursor over them and clicking the mouse button or typing <ENTER>. The object's name will then appear above the cursor coordinates and these coordinates will change to reflect the precise position of the object. Map Menu -------- The Map menu appears at the bottom of the screen in Map mode. Most menu items are also found in the Guide mode described above and function in the same way. Two new items not found in Guide mode are discussed below. Animate- Selecting Animate will display the Animate menu and begin the An- imate process. In this mode, the planets will be displayed briefly against the background stars for the current date, then the date will be increment- ed by one day and the planets' positions will be updated. To pause the an- imation, select stOp by typing 'O' (not 0) or click the mouse button over the item. To resume the movement, select cOntinue. Use Animate to see where the planets will be on any given date. When animation is paused the display date may be changed at will. The current display date next to the cOntinue item will be displayed lighter and can now be changed. To decrease the display date by one month, type '-' or click the left mouse button over the month value. Type '=' or click the right button to increment the month. Type '[' or click the left button over the day to decrease the day. Type ']' or click the right button to increment the day. Type ',' or click the left button over the year to decrease the year. Type '.' or click the right button to increase the year. The planet positions are updated each time one of the date fields is changed. Select cOntinue to resume the ani- mation with the new display date. Note: In the Demo version, you can not Animate forward into the next year or back into the previous year. The animation normally proceeds into the future but can also work backwards. To animate back into the past, type 'P' or click the left button over this item. To animate into the future, type 'F' or click the right button. An up arrow will be below the word Past if animation is proceeding backward and will be below Future when animation is proceeding forward. The rate at which the planets are updated can be varied. To slow the update process down type 'S' or click the left button over these items. Typing 'Q' or clicking the right button will speed up the display. These commands may be repeated to change the speed even more. An arrow appears below these com- mands to indicate the relative speed of update. The slower you make it, the further to the left the arrow will appear. The arrow will move to the right as you increase the update speed. Normally, as the planets proceed across the screen, their last positions are blanked from view. However, you can disable the blanking for any single planet so that it leaves a trail. This is useful for studying retrograde mo- tion of a planet or for defining the ecliptic in the case of the sun. To en- able the trail of a planet, first select stOp to pause the display. Then type 'T' to sequence through the list of objects. Just above the word Trails will appear the name of the object which will leave a trail. Once the de- sired object appears select cOntinue to resume the animation. Mouse users can sequence through the list backward by clicking the left button over Trails and forward by clicking the right button. When animation resumes, a trail will be left behind where the planet has been. To leave a trail of another planet superimposed over the first, follow the above procedure for the second object and start over with the initial display date or simply run the animation backwards for this object. To dis- able the trails, sequence through the list until no object name appears above Trails. Finally, to exit Animation mode and return to Map mode, select eXit. Zoom- Zoom mode allows you to zoom in on a particular area of the display to enlarge the size of a constellation or resolve a densely packed group of objects. The zoom "factor" is initially 1.0 in Map mode, meaning that the whole sky is displayed. To enlarge a particular portion of the display, type 'Z' or click the right mouse button over the Zoom item. The zoom "factor" will change to 2.0 and that value is indicated in the upper right corner of the screen. All objects in the display are erased and the objects within the new view range are redisplayed. The objects will not appear any larger but will be slightly brighter and more colorful. The separation between them is now twice as big, and collections of objects (i.e. constellations) will appear bigger. Notice that the right ascension and declination coordinates below and to the right of the map have changed to reflect the new view range. Just below the zoom "factor" indication in upper right, four arrow buttons are now visible. These are scroll buttons that allow you to scroll the dis- play window to different areas of the sky. When the zoom "factor" is 2.0, you can see only 1/4 of the whole sky. The initial center of the display is the same as the center of the display with zoom = 1.0, with an RA value of 12.0 hours and Declination of 0 degrees. However, now you can only see be- tween 6 and 18 hours of RA and -45 to +45 degrees of declination. To see areas of the sky beyond this, you use the scroll feature. To see areas of the sky to the left (greater RA values) of the current view, click the mouse on the left scroll arrow. If you don't have a mouse type ','. To scroll to the right, click the right scroll arrow or type '.'. To scroll up to see ob- jects of greater declination, click on the up scroll arrow or type '='. To scroll down click the down arrow or type '-'. You can use the scroll feature repeatedly to see any area of the sky. When you reach the edge of the sky, for example you reach an RA value of 0 on the right side of the display when scrolling right, you can not scroll any further in that direction. The appropriate scroll button will darken to in- dicate this. If you have a slow machine or it lacks a math coprocessor, it is recommended that you turn off the display of constellation lines and neb- ulae if you are going to make several repeated scrolls. This will substan- ially speed up the scroll process. When you arrive at your new location you can turn them back on if desired. To zoom in more, type 'Z' again or click the right button again. Each time you zoom in the zoom factor doubles up to a maximum of 128.0. Zooming in again at a factor of 128.0 takes you back to zoom = 1.0. You can also zoom out by a factor of 2 by typing 'Y' or clicking the left mouse button while over the Zoom item. Zoom mode can be used along with Animate. For example, to see the positions of planets at a conjunction (very close grouping of one or more planets), first zoom in to an appropriate zoom "factor" and then scroll to the pos- ition of the sky where the conjunction occurs. Now select Animate and pause the display. Finally, set the month, day, and year to the date of the event. The planets should appear on the screen similarly to the way they actually appear in the sky. You can identify the objects by clicking on them as described earlier if necessary. Note: a very nice conjunction of Venus, Mars and Jupiter (and the moon, too) occurred on June 15, 1991. To leave Map mode and return to the Main menu, type 'X' or click on eXit. The TeleScope View ------------------ TELESCOPE VIEW: The telescope view combines features of Guide mode and Map mode. This mode is designed to simulate a view of the sky as seen through a telescope. The look of this mode is very similar to that of Guide mode. A circle is displayed on screen which represents the 'field of view' of the telescope at the current settings of view direction and zoom factor. Initial- ly, the view direction is the zenith with a zoom factor of 1.0. This is eq- uivalent to what would be seen in Guide mode at the current date and time. In other words, the circle represents the horizon, with the center of the circle corresponding to looking straight up. Telescope differs from Guide mode in some important respects. The display be- low the current date and time in the upper right corner of the screen, shows the Right Ascension and Declination coordinates and the width of the current field of view. The current zoom factor is also displayed- 180 degrees, i.e. horizon to horizon. Note that Telescope mode is not dynamic like Guide mode. Although the current date and time are constantly updated, they have no effect on the display. Telescope mode allows you to zoom in to a particular location without the distortion inherent in Map mode when viewing away from the celestial equator. The Telescope mode has N, S, E, and W directions around the circle as in Guide mode. These correspond to directions from the center of field of view. Thus, a point above the center of view is north of center of view. A point to the right of the center of view is west of the center of view. Note that when the center of view is very near the north or south celestial pole, these dir- ections are meaningless. Telescope Menu -------------- Most menu items in Telescope mode are the same as and work similarly to those in Guide or Map modes. However, two of these require further comment. Location- This selection works differently than it does in Guide mode. Here, the location refers to the coordinates of the center of view. To change the declination value of the center of view, type '-' or click the left button over the current value to decrement it, or type '=' or click the right button to increment it. Type '<' or click the left button over the Right Ascension value to decrement it or type '>' or click the right button to increment it. Select Update to display the field with the new values. Select eXit to accept the new values and return to the Telescope menu. Zoom- This is essentially the same as Zoom in Map mode. Type 'Z' or click the right button over Zoom to zoom in by 2 times. Type 'Y' or click the left but- ton to zoom out by 2 times. The field width and zoom factor in the upper right hand of the screen change to reflect the new settings. The Settings ------------ SETTINGS: There are several variables used in SKYCHART that depend on location, preferences, or hardware. These variables can be customized by the user in this section. Once set, these will then become default settings each time the program is run. Select Settings from the main menu to change them. Lattitude- The observer's lattitude is used in the Guide mode to determine what portion of the sky is visible at any given time. You should enter your lattitude in so that Guide mode will be accurate for your location. Type '-' or click the left button over the lattitude value to decrement it or type '=' or click the right button to increment it. Longitude- The observer's longitude is also used in Guide mode for proper display of the sky. Type '<' or click the left button over the value to dec- rement the value or type '>' or click the right button to increment it. Longitude must be between -180 degrees (east longitude) and +180 degrees (west longitude). Zero degrees longitude runs through Greenwich, England. Daylight Savings Time- Skychart must know if you observe Daylight Savings Time in order to properly display the sky in Guide mode. Select automatic mode to have Skychart automatically keep track of DST. In Auto mode, the program assumes that DST is in effect from the 1st Sunday in April to the last Sunday in October. If your area has different dates for DST or does not use it at all, you must manually turn DST mode on or off. Type 'D' or click a button over the displayed mode(not the letters DST) to cyle through the choices. 'A' = auto, 'N' = DST off, 'Y' = DST in effect. Time Zone- Skychart must know the time zone of your location. Valid time zone values range from -12 to +12, with the negative values corresponding to locations east of Greenwich, England and positive values for locations to the west. Type 'Z' or click the right button over the value to increment it, or type 'Y' or click the left button to decrement it. Exit- To leave the Settings menu and return to the main menu, select 5. eXit ---- Finally, select eXit from the main menu to exit SKYCHART and return to DOS. ------------------------------------------------------------------------------ UTILITIES --------- The Catalog utility that comes with Skychart is used to generate the star database. The database supplied with Skychart consists of over 45,000 stars. This includes all stars brighter than 8th magnitude. When you run Skychart for the first time, all 45,000 stars visible within the current view will be displayed. You may wish to have Skychart display fewer stars than this, how- ever. You might want to do this to unclutter the display or to speed up the rate at which the screen is updated. Also, since a computer screen cannot display stars with magnitudes varying from -1 to 8 magnitude with accurate representive brighnesses, it can be very hard to distinguish the bright stars from the dimmer ones with all the stars displayed. You can decrease the number of stars displayed in two different ways. One way is to change the limiting magnitude of displayed stars by selecting the Mag- nitude option from the Guide, Map, or Telescope menu. By reducing the limiting magnitude from the default 8.0 to a lower value will decrease the number of stars displayed. This will result in decreased clutter and better contrast be- tween bright and dim stars but will not substantially speed up the display updates. To speed up the display, you must actually decrease the size of the database. You can do this by running the Catalog utility, from outside the Skychart program. From the DOS prompt, type CATALOG and press enter. you are asked to enter a new limiting magnitude for the database. Valid magnitudes range from 1.0 to 8.0. The program then begins to generate a new database which contains only those stars as bright as the limiting magnitude. A progress report of the process is given near the bottom of the screen as a percentage of the whole catalog which is complete. When the catalog is 100% complete, the num- ber of stars retained in the new catalog is given at the bottom of the screen. You may now restart Skychart with the new catalog in effect. Many fewer stars will now be displayed, and update speed will be accordingly increased. Catalog can be used as often as you wish. You can restore the original data- base with all 45,000 stars by running Catalog with a limiting magnitude of 8.0.