Magnum One

home *** CD-ROM | disk | FTP | other *** search

/ Magnum One / Magnum One (Mid-American Digital) (Disc Manufacturing).iso / d26 / skyplot.arc / SKYPLOT.DOC < prev next >

Wrap

Text File | 1987-10-11 | 31.2 KB | 785 lines

S K Y P L O T The Planetarium Simulator Gerald M. Santoro 148 W. Hamilton Ave. State College, PA 16801 USER DOCUMENTATION Version 2.0/2.1 -- Copyright 1987 1. Preliminaries ----------------- 1.1 Introduction ----------------- 1.1.1 Quick Description ------------------------ SKYPLOT is a program that simulates many of the operations of a Planetarium. In particular, when given a date and time (specified in Universal Time and between the years 1975 and 2500), a position (specified in longitude and latitude), and a direction (N-E-W-S), the program will produce a simple plot of the sky. This plot will contain the Sun, Moon and planets (assuming that these are in that part of the sky at the specified time), and as many stars as are in the star database SKYPLOT.DAT. These stars are taken from the Yale Catalog of bright stars. Once a plot is produced the user has a number of options. These include changing the parameters (date, time, position, direction), examining the Right Asencion and Declination of Solar System objects, and dumping the data to an attached printer. SKYPLOT has been developed on an IBM PC/XT with an 8088 processor. The compiler utilized was Microsoft Quickbasic 3.0. Since SKYPLOT is a graphics-based system your computer must be able at at least emulate IBM CGA graphics. (However CGA-compatible composite-video displays should work as well.) SKYPLOTE is the EGA version of SKYPLOT and requires an EGA or EGA compatible graphics emulation. Although the size and aspect of the display are the same between CGA and EGA, the EGA resolution is much finer and the display is in color. If you have any choice at all you should opt for the EGA version. 1.1.2 Statement of Authorship ----------------------------- SKYPLOT was originally written as a private endeavor of Gerald M. Santoro during the Fall - 1983 on a TRS-80 Color Computer, and converted to the IBM-PC series during March, 1985. Extensions to the graphic symbols for solar system objects and to the year ephemeris range were made by Robert Sheaffer. Along with a few other extensions and changes this version was released as Version 2.0 in the fall of 1987. SKYPLOT is distributed according to the principles of 'User-Supported Software'. These principles state that the value of a given software package can be best determined by the end user. Therefore, in accordance with these principles all persons are encouraged to copy, distribute and use the program. A donation of $10.00 is requested by the author only if the end user deems the program worthy and wishes to support the creation of more software. Please note that a donation is NOT neccessary to posess, use, copy or distribute SKYPLOT. This condition is retroactive to all previous versions of the program. On the other hand I will gladly accept all contributions and will use them to support further enhancements to SKYPLOT. The only limitations imposed upon the distribution of the software are that (1) the software not be distributed in modified form without the expressed, written consent of the author, (2) that the copyright notice, statement of authorship, and request for donation remain intact in all versions of the software, and (3) that no charge be made for distribution of the program other than that to cover reasonable handling and mailing costs. If you have any questions regarding these limitations, please feel free to write to me. 1.1.3 Obtaining a Copy of SKYPLOT ---------------------------------- As with other programs distributed under the 'User-Supported' software concept, it is hoped that most of the distribution of SKYPLOT will occur via computer clubs and other user's groups. However, if none of these channels are available, a copy of the program may be obtained by sending a 5.25" or 3.5" DS/DD floppy diskette, a preaddressed, diskette mailer, and $10.00 (to cover handling and postage), to the following address: Gerald M. Santoro 148 W. Hamilton Ave. State College, PA 16801 Please note that any diskettes recieved without a preaddresed, diskette mailer and the $10.00 handling fee will be ignored. (Alas, my time is really spread thin.) Unlike previous versions of SKYPLOT, the BASIC source program will not be distributed with the executable program and data files. If you want to obtain a copy of the source program I ask that you write me and send a preformatted disk as per the above. I will likely give you the source but I want to protect the contributions and reputations of all of the program contributors. 1.1.4 Statement of Purpose --------------------------- I wrote SKYPLOT as a mental exercise stemming from my lifelong interest in Astronomy. I am distributing it as a 'User-Supported' program in the hope that it will stimulate a similar interest in others. As a point of historical interest, I wish to mention that the original version of SKYPLOT premired during the 1983 Open House ceremonies at Allegheny Observatory of the University of Pittsburgh. Indeed, as a 'would-be Astronomer turned Computer Scientist', it was one of the proudest moments of my life to have this program presented to the public by some of the best professional Astronomers of our time. Therefore please regard SKYPLOT as an educational tool for discovery in observational Astronomy. The program puts the entire sky at your disposal between the years 1975 thru 2500. Explore and enjoy! 1.1.5 An Important Note ----------------------- It was pointed out to me, during the final testing for SKYPLOT, that this program would be ideal for the generation of astrological charts and other such nonsense. I wish to point out that the program is NOT intended for that purpose, and anyone wanting to use it for that purpose is better off reading Tarot Cards or looking for good investment bridges. 1.1.6 Dedication ----------------- This program is dedicated to the people at Allegheny Observatory who made my brief tenure as a 'professional' astronomer so enjoyable and to my wife Kathy, who has been very supportive of my crazy obsession with Astronomy. 1.2 Universal Time ------------------- When SKYPLOT requires a date and time they must be specified in Universal Time. Universal Time is essentially Greenwich Mean Time, or time as measured from 0 degrees longitude (which happens to run through Greenwich, England.) Therefore, you must convert your local mean time to Universal Time. This is quite easy and simply requires that you add or subtract a certain number of hours from local mean time, depending on your time zone. For example, if you are in the Eastern time zone of North America, you would normally add 5 hours to local mean time to get Universal Time. (During Daylight Savings Time you would add 4 hours.) Thus 12:00 noon local time EDT corresponds to 17:00 UT. Keep in mind that the date changes when you cross 24:00 (otherwise known as midnight). Thus 21:00 on January 10 (9:00 pm) EDT corresponds to 2:00 (am) on January 11 UT. A simple conversion chart follows for the Western Hemisphere. (My apologies to persons in the Eastern Hemisphere, but I did not have the data readily at hand.) Conversion to Universal Time (North America -- USA) Time Zone Conversion ============================================================ Eastern Add 5 hours. (Add 4 hours for DST) Central Add 6 hours. (Add 5 hours for DST) Mountain Add 7 hours. (Add 6 hours for DST) Pacific Add 8 hours. (Add 7 hours for DST) 1.3 Files on the SKYPLOT Disk ------------------------------ The following files should be contained on your copy of the SKYPLOT disk: SKYPLOT.EXE - The compiled program for CGA display. or SKYPLOTE.EXE - The compiled program for EGA display. SKYPLOT.DAT - The file of stars to be plotted. (Initially the same as STARS.450 SKYPLOT.DOC - This documentation file. OBJECTS.DAT - Sample objects file. STARS.250 - Star data to magnitude 2.50. STARS.350 - Star data to magnitude 3.50. STARS.400 - Star data to magnitude 4.00. STARS.450 - Star data to magnitude 4.50. STARS.500 - Star data to magnitude 5.00. (This data came from the Yale catalog of bright stars> 1.4 The Algorithms ------------------- The algorithms used in SKYPLOT were derived from the calculations given in the book "Practical Astronomy With Your Calculator" by Peter Duffett-Smith. 2. Running SKYPLOT ------------------- 2.1 Starting the program ------------------------- To start SKYPLOT you should do the following: 1. Boot your system with DOS. (At least Version 2.0.) 2. Place the SKYPLOT disk in drive A: (or if you have a two disk system you can put the SKYPLOT disk in drive B: and change the default drive to B:). 3. Type SKYPLOT <cr> where <cr> is the RETURN key You will then be shown an introductory screen that identifies the program and author, presents a copyright notice, and specifies the conditions under which the program may be copied and/or used. You are instructed to press any key to proceed with the program. You are then at the 'Enter Parameters' stage. 2.2 Exiting form SKYPLOT ------------------------- To exit from SKYPLOT and return to DOS, you should press [Ctrl]- [Break] a few times. 2.3 Parameters --------------- The program parameters are information SKYPLOT needs to create a plot of the sky. These parameters are grouped into the categories (1) date/time, (2) location, (3) direction, and (4) options. Please remember that the date/time must be entered in Universal Time. Each of the parameters will be described in detail below. To illustrate this better I will provide an example. If you have an appropriate computer handy you should follow along with the example. This example, as well as the description of the display following, will make MUCH more sense if you run this on a computer as you are reading it. 1. Year (1975-2500) The year must be entered as a 4-digit number. Valid years are in the range 1975-2500. This is because of the seed values for Siderial Time and the planetary positions in the program. Example -- 1985 2. Month (1-12) The month must be entered as a 1 or 2 digit number in the range 1-12, where 1 corresponds to January and 12 corresponds to December. Example -- 3 3. Day (1-31) The day must be entered as a 1 or 2 digit number in the range 1-31. The program does not care about months with fewer days than 31. If you ask for February 31, 1985 you will actually get the sky for March 2, 1985 (of course the display will lie and say February 31, 1985). Example -- 16 4. Hour (0-24) The hour must be a number in the range 0-24. Decimal fractions of hours are permitted. (Again remember that Universal Time is required, and that it may have an effect on the value for Day.) Example -- 22 5. West Longitude (0-360) The Longitude of the observer must be entered in degrees west from the Prime Meridian, (0 degrees). Example -- 80 (the rough West Longitude of Pittsburgh) 6. Latitude (-90 to 90) The Latitude of the observer must be entered in degrees. For southern latitudes preceed the value with a minus sign (-), for northern latitudes just the value will suffice. Example -- 40 (the rough Latitude of Pittsburgh) 7. Horizon (N-E-S-W) This is the compass direction of the horizon upon which the plot is to be centered. Either upper or lower case may be used. Example -- W 8. Option 1 = Solar System Only 2 = Solar System and Stars (naked-eye planets only) 2 = Solar System and Stars (telescopic planets also) 3 = Also plot objects from user-supplied file This selects the plotting option for the plot. Option 1 will cause only the Solar System objects to be plotted. This is very fast and is nice if all you are concerned with is the planetary groupings with respect to the horizon. Option 2 will plot the Sun, Moon and all naked-eye planets, as well as the stars found in the file SKYPLOT.DAT. You can control the limiting magnitude of the stars plotted by copying the sppropriate STARS.* file to be SKYPLOT.DAT. (Copying is preferred over renaming so you don't lose the original data.) For example, to plot stars to a limiting magnitude of 4.00 (which I have found to show constellations best) you would issue the dos command: COPY STARS.400 SKYPLOT.DAT Bear in mind that there is a tradeoff between magnitude and plotting speed. In other words the files with brighter limiting magnitudes will plot faster because there are fewer stars to plot. Option 3 will do the same as option 2 but it will also plot the telescopic planets Uranus, Neptune and Pluto. Option 4 will do the same as option 3, however it will also open a user-supplied file and plot the objects whose positions are found there. A description of this process may be found later in this document. If you choose this option, SKYPLOT will ask you for a file name. For the sake of this example, enter 2. 2.4 The Plot of the Sky ------------------------ Upon entering the last parameter, SKYPLOT will generate a plot of the sky at the date/time specified, as seen from the longitude and latitude specified, centered on the compass direction of the horizon specified. If you have followed the example you should see a plot of the western sky as seen from Pittsburgh Pennsylvania on March 16, 1985. This happens to be the evening of one of the best eastern elongations of the planet Mercury. The plot area itself is the dome-shaped area on the display. It is dome-shaped to reduce the distortion generated in trying to plot a curved surface onto a flat surface. (This is apparant in Mercator projection maps where the island of Greenland appears as large as North America. This distortion, if not corrected, would make star groupings and constellations at the top of the plot unrecognizable. As it is the correction method is not optimal and some distortion will still be noticed. (I am working on the problem and version 3.0 should have it corrected!) One way to think of the plot area is in terms of a planetarium dome. If you were to project the sky on the inside of a planetarium dome, then split the dome in half along a line perpendicular to the direction you are looking, and you eliminated the half closest to you, you would roughly see what is displayed in the plot. (If you are not looking at a plot right now this probably will not make much sense.) The vertical tic marks along the sides of the plot indicate 10 degree increments of altitude, with zero degrees along the bottom line and 90 degrees at the top of the 'dome'. The horizontal tic marks along the horizon indicate increments of 30 degrees in azimuth. A ststus line just below the tic marks indicates the compass headings for each tic mark. The middle status line displays the option selected, the latitude, longitude, year, month, day, universal time, and local siderial time for the plot. The Sun is indicated by a round circle towards the lower central part of the display. Planets are indicated by little circles, with an identifying number printed directly below the circle at the bottom of the screen. This number identifies the planet by its order outwards from the Sun. Thus Mercury is a 1, Venus a 2, Saturn a 6, and so on. The Moon is indicated by a symbol that roughly also indicates its phase. Since the resolution of the plotting area is limited by the overall 640 by 200 resolution of GW-BASIC, you must keep in mind that the symbol indicating the solar system object is only approximating the real position. The stars are indicated by three levels of star marker. This is to give some indication of the relative brightness of the stars. This has been fudged slightly in the SKYPLOT.DAT star database to allow familiar constellation outlines to be more easily apparant. Upon completion of the plot the program will beep briefly to indicate that the plot is finished. 2.3 SKYPLOT Options Menu ------------------------- If you now press any key, the plot will be erased and the SKYPLOT Options Menu will be displayed. This menu will allow you to alter the parameters and replot the sky. Thus allowing you to 'play' with the sky. In the next section, a number of examples will demonstrate the use of these options, however a brief explaination of the options is provided immediately below. 1. Change Year This option changes the year of the plot. 2. Change Month This option changes the month of the plot. 3. Change Day This option changes the day of the plot. 4. Change Hour This option changes the hour of the plot. (Remember that the hour must be in Universal Time. 5. Change Longitude This option changes the west longitude of the plot. 6. Change Latitude This option changes the latitude of the plot. 7. Change Horizon This option changes the horizon on which the plot is centered. 8. Change Plot Option This option allows the user to change the plot option. 9. Examine Solar System Data This option may be used to produce a view on the display, or print to an attached printer the Right Asencion and Declination for the Sun, Moon and Planets. These values may be used to verify the accuracy of the projected positions against a reference source such as the American Ephemeris and Nautical Almanac. The accuracy of the positions calculated by the program is rough, and will only be within about a degree of their true positions. This degree of accuracy is adequate because (1) the pixel resolution of the plot is only that good, and (2) to achieve greater accuracy (even though you could not see it) would slow the program down. 10. Plot Sky This option is used to replot the sky after one or more of the parameters has been changed via the Options menu. 11. Enter All New Parameters This option may be used if you know that you are going to change most or all of the parameters, and do not want to do it one parameter at a time with the Options Menu. 12. Exit to DOS This option allows the user to exit SKYPLOT and return to DOS. The users DOS disk with the COMMAND.COM file should be on a disk in the default system drive. 2.5 Examples with the Options ------------------------------ These examples will assume that you are in front of a computer and have run the example described under the Parameters section above. If you have not done this you should now enter the following values: Year - 1985 Month - 3 Day - 16 Hour - 22 West Longitude - 80 Latitude - 40 Horizon - W Option - 2 This set of parameters will display the western sky just before sunset at the approximate time of greatest eastern elongation of Mercury from the Sun. In addition, the presence of Mars and a very brilliant Venus made this a particularly beautiful planetary grouping. Having observed and photographed this grouping I can testify that the display produced by SKYPLOT does not truly do justice to the real thing seen in person! Now lets try some of the options for a demonstration of their use. Press the spacebar to go to the Options Menu. Select option 8 to change the plot option, then specify option 1 to plot only the Solar System objects. SKYPLOT will acknowledge the option by clearing the screen and redisplaying the Options Menu. Now you may enter other options, however for the sake of this example enter option 10 to replot the sky. Plotting only the Solar System objects causes the plot to be completed very quickly. Now press the spacebar again and select option 4 to change the hour. Enter 23 for the hour and select option 10 to replot the sky. Notice that the Sun has set. In fact, it has just set, but the program does not account for twilight, or for the fact that the Sun is large enough to be in a condition of partial rising or setting. To SKYPLOT an object is essentially a point on the sky and is either visible or not. Now press the spacebar and select option 3 to change the date. Enter 20 as the date, then select option 10 to redraw the plot. You should see the Sun again because its motion along the ecliptic is taking it northward, and it is now above the theoretical horizon. You should also now see the Moon, its daily motions having taken it past new phase to emerge in the evening sky. You may want to advance another day or two to watch the Moon's motions. The process should be fairly obvious by now - pick one or more options and replot the sky. You will also notice that Venus is moving towards Mercury, and both are rushing towards inferior conjunction with the Sun. Now press the space bar and select first option 7 to change the horizon of the plot. Specify S for the southern horizon. Then select option 9 to plot both Solar System objects and stars. Select option 10 to replot the sky. You should be faced with a winter sky dominated by Orion and Canis Major. Press the spacebar to bring up the Options Menu and select option 5 to change the longitude for the plot. Since you are currently at longitude 80 West (All longitudes must be in degrees West from the Greenwich meridian) entering a value greater than 80 (such as 100 or 120) and replotting should show the constellations shift to the least. Liklewise, entry of a smaller number (such as 50 or 60) and replotting should produce a shift to the west. As mentioned before, this is the reason why Universal Time is used rather than local time. Accounting for local time zone changes would be too complicated for most user to deal with. After playing with the longitude, select option 6 to change the latitude for the plot. Since you are currently at latitude 40 degrees north, entering a value lower than +40 will result in the constellations shifting north in the plot. Likewise entering a value greater than +40 will result in the constellations shifting south. If you have a printer attached to LPT1: on your PC, you can select option 9 and get a printout of the Right Ascention and Declination for the Solar System objects as calculated by SKYPLOT. At very least you should pick option 9 to examine their positions on the display. This may help to determine how close the program would place two nearby objects. As mentioned earlier, these values should be within about 1 degree of the actual position of the object. A good book to verify this is the American Ephemeris and Nautical Almanac, which is available in the reference section of many University and public libraries. Option 11 may be selected to enter all new parameters, just in case you find this less of a hassle than doing it option by option. Option 12 may be used to exit from the program to DOS. (Your PC will likely expect to see COMMAND.COM when it exits from SKYPLOT.) 2.6 Plotting Objects from a User-Supplied File ----------------------------------------------- As as extra feature, SKYPLOT allows the user to plot other objects along with the Solar System and stars. To do this the user must know the Right Asencion and Declination of the object. Of course, like most objects in the sky, this information will only be relevant for a particular date -- so bear this in mind when creating the plot. The data is entered into a file with any simple ASCII text editor (EDLIN will suffice). It is in the form of 5 parameters. These are (1) the hour of Right Asencion, (2) the minutes of Right Asencion, (3) the degrees (positive or negative) of Declination, (4) the minutes of Declination, and a marker symbol indicator. The marker symbol indicatior is used to specify a marker which is used to plot the object on the sky. Four marker symbols are available, they are: Marker Marker Symbol Indicator -------------------- ----------------------------------- alpha 6 beta 7 gamma 8 delta 9 The Marker is one of the first four letters of the Greek alphabet. A given marker may be used more than once. This could be useful if you want a rough track of an object (seen against the stars) over a range of dates (you could use the same symbol with different positions). Again, note that the program dosen't care if the data you provide is false. If you create a file, say Z.Z, and put in the position of a comet for May 1, 1975, then you plot the sky for August 20, 1990 and choose option 3 with the file Z.Z, SKYPLOT will proceed to plot the object just where you said it would be on May 1, 1975. As an example, the file OBJECTS.DAT is provided. This file will serve to demonstrate the format you must observe for the object file. Note that the last line must contain the value 999. This file will plot the alpha, beta, gamma and delta symbols in northwest Orion. Pick an appropriate winter sky and choose option 3 with the file OBJECTS.DAT and you will observe this. This technique was successfully used to plan for the 1986 apparition of Comet P/Halley. It enabled observing expiditions to be organized and carried out well in advance of the comets arrival. 2.7 SKYPLOT.DAT - The Stars Database ------------------------------------- The stars database should be a copy of one of the STARS.* files according to your desire for limiting magnitude. I find STARS.400 to be the best one overall for constellation identification. Given normal CGA resolution it is probably unwise to add many more stars than this. When I have built in EGA graphics this problem may be resolved. The format of this file is the same as that for the objects file. If you wish to add stars to it you can use any vanilla ASCII text editor. (EDLIN works fine although it is a horrible editor!) 3.0 Concluding Statement ------------------------ I hope you enjoy the program as much as I've enjoyed creating it. I know that there are other similar, and in some cases much better, planetarium simulators on the market. However this one should add a simple but different twist to the genre. In conclusion, please explore and enjoy, and try to take some time out to experience the Real Thing! Gerry Santoro State College, PA -- (Happy Valley) September 13, 1987