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Astropack Astronomical Tools: Reference Manual Version 2.0 (Aug. 1988) 2 Although this program and manual are copyrighted, they may be freely copied and distributed provided that they are not modified in any way and that the program is not distributed without this file. (c) 1988 Graham Denham 3 Contents: Licence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Registration Form . . . . . . . . . . . . . . . . . . . . . . . . 5 The program: INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 6 SETTING UP . . . . . . . . . . . . . . . . . . . . . . . . . 6 TIME CALCULATIONS . . . . . . . . . . . . . . . . . . . . . 7 POSITION CALCULATIONS . . . . . . . . . . . . . . . . . . . 8 CONVERSIONS . . . . . . . . . . . . . . . . . . . . . . . . 9 PRINTING . . . . . . . . . . . . . . . . . . . . . . . . . . 9 A NOTE ON PRECISION . . . . . . . . . . . . . . . . . . . . 10 4 Licence: This product is not free software. Instead, it is being distributed as user-supported software. This means that if you decide to use the program, you should register your copy with me by sending your name, address, and $15 (1) to Graham Denham 11611 50 Ave. Edmonton, AB Canada T6H 0J7 In return for your support, as a registered user you will receive notice of future versions of Astropack and of the release of any related products. The fee registers you to use this and any future versions of the program. Additional copies and updates are available to registered users at the cost of a diskette and postage. Once you register, please feel free to send questions and suggestions. Also, please contact me if you are interested in the C source code of this program. Remember that the future of user-supported software depends on YOUR support. ----------- 1 Either U.S. or Canadian funds accepted. Registration form: (Astropack, ver. 2.0 and up) NAME: _____________________________________ ADDRESS: _________________________ _________________________ _________________________ POSTAL CODE / ZIP: _________ Do you want your name placed on the mailing list? Y N 6 INTRODUCTION: Astropack is a general-purpose mathematical astronomy program. It combines various time and position calculations that are often tedious or difficult to do by hand. The program is intended for astronomy hobbyists, students, or anyone else who might be curious about when the sun will set next week, or how far it is from Stockholm to Sacramento. For users with serious requirements, Astropack provides reasonably accurate values that will supplement those that an astronomical almanac offers. It is especially valuable if an almanac for the appropriate time period is not available. If you have a standard printer, the program can also print tables of values for any time periods. Note: this manual can be printed on most printers from DOS by typing COPY README.DOC LPT1: SETTING UP: To start the program, simply type ASTRO. The program will load and you will see the main menu screen. To select an item from any of the menus in the program, use the cursor keys to move the pointer, and then press Enter. You can also escape from a menu to the previous one by pressing Esc. The first thing which you should do when you run Astropack is to tell the program what timezone you are in. All of the times that you will enter will be local times that depend on your timezone. It is therefore important to set your timezone before doing any calculations. The initial menu screen will display a flashing reminder to this effect in the event that you forget. To set the timezone, select the first item on the main menu. You will then see the setup menu. Once again, take the first item on this menu, and the program will prompt you for your timezone as the separation in hours from Universal Time. The table provided will help you if you are not certain about the number of hours. Many calculations also require the observer's latitude and/or longitude. If you know your latitude and longitude, this will present no problem. If not, you can do one of two things. First, you could determine your position from maps or charts. Alternately, Astropack can supply your approximate latitude and longitude if you are located in or near one of several major cities. If approximate values are acceptable for your purposes, this latter method is easy and saves time. To use this built-in feature of the program, select the second item on the setup menu: "Set Location". The program lists about 50 7 cities in Canada, the United States, and elsewhere. When you choose one, the program will store its latitude and longitude as its default values. This means that when you are prompted for your latitude or longitude later, you can just press Enter to use the value for your city. (It should be noted, however, that these values are necessarily somewhat imprecise. In large metropolitan areas, the coordinates usually refer to the downtown area. In the Los Angeles area, for example, the longitude varies by about 1/3 of a degree from one end to the other. If you require more precise results, you should determine your position from a map.) TIME CALCULATIONS: These include the determination of Greenwich Sidereal Time, Local Sidereal Time, and Julian Date. You can get to the time calculations menu by selecting the second item on the main menu. Once you select a function on this menu, Astropack will prompt you for any necessary values. You will probably discover one of the program's useful features at this point. When you have to enter a value for a calculation, the program usually gives you a default value which you can use by just pressing Enter. This default is either the value that you last used, or the result from a previous calculation. The feature is designed to make it unnecessary for you to keep re-entering the same value, or to write down values that are needed only for further calculations. It is often desirable for you to be able to enter values directly as degrees, minutes, and seconds, or as hours, minutes, and seconds, rather than having to convert them to decimal. Accordingly, the program usually requests that you enter numbers in the form DDD.MMSSss or HH.MMSSss. This means that you enter the degrees (or hours) first followed by the decimal, and then the minutes, seconds, and any fractions of seconds. For example, one would enter 30 deg., 21 min., 15.3 sec. as 30.21153. Similarly, one would enter 1 h, 3 min., 45 sec. as 1.0345. Notice the zero before the three in this example: it is necessary to preserve the place value of the decimals. If you select "Ephemeris" from the Time menu, Astropack will print or display a table of sidereal times. First, you are asked whether you want the table to be produced on the screen or on the printer. Hit 's' for screen or 'p' for printer. (Before you print for the first time, please see the section on PRINTING, p. 9) Next, the program asks you for the start and end dates, as well as the number of hours between each entry on the table. 8 POSITION CALCULATIONS: This category actually includes rise, set, and transit calculations as well as position. An unrelated but interesting function is also grouped here for convenience - the determination of the great-circle distance between any two points on the Earth. The first item on the Position menu allows you to determine the position of the sun for any date and time. It gives the apparent rectangular coordinates in addition to the right ascension and declination. The second and third items let you calculate the times at which the sun or some other object rises, transits, and sets. The calculation for the sun automatically finds the sun's position first, whereas you have to specify the position in the other calculation. For example, to find the approximate rise, set, and transit of Mercury given its position, you would select "Any Times" from the Position menu, enter the date, your position, and its position. (The program asks for an object's position in equatorial coordinates. If you have its ecliptic coordinates instead, see the section on conversions, p. 9). Once again, please remember to set your timezone. If you do not, the results from these calculations will not be in your local time. All of the "rise, set, transit" calculations take atmospheric refraction into account. The sunrise time is for the ascending limb of the sun, and the sunset time is for the descending limb. These calculations use only one position value, although they are generally accurate to within five minutes of the actual, observed rise, set, or transit time. Note that if the position of the object is changing rapidly, then the error could be somewhat greater. You can also produce a table of sunrise, transit, and sunset times using "Ephemeris". This function works in essentially the same manner as "Ephemeris" on the Time menu (see p. 7). It asks you whether you want the table sent to the printer or the screen, and then it asks for the time period of the table. The second-last item on this menu, "Distance", lets you calculate the distance between any two points on the Earth and the heading from the first point to the second. It gives you the great-circle distance (the shortest distance along the surface of the Earth) rather than straight-line distance (i.e., through the Earth). The program will prompt you for the first location, for which you can use your default latitude and longitude. It then requires the coordinates of the second location, which you can find on a map or in the table of cities within the program (for this, see pp. 6 - 7) The heading which the function returns is measured in degrees, clockwise from north. 9 CONVERSIONS: Astropack can convert between ecliptic and equatorial coordinates. To make a conversion, select "Conversions" on the main menu. Choose the first item on the Conversions menu if you wish to convert a pair of equatorial coordinates to ecliptic coordinates. The function will let you use the default equatorial coordinates if you wish, which is useful if another calculation has given you equatorial coordinates and you would like to convert directly. The second menu item lets you do the complementary conversion: ecliptic to equatorial coordinates. You must enter the ecliptic latitude and longitude, and then the program will return the equatorial coordinates. As usual, it also stores them as the default values for your next calculation. Finally, you can calculate the altitude and azimuth of an object from its coordinates with the third item on the menu. When you use this feature, the program asks for a date, time, and position, as well as the equatorial coordinates of the object. It returns the altitude and azimuth in degrees. PRINTING: Before you can print any tables, it is necessary to configure the printer. This can be done by selecting "Printer Configuration" on the Setup menu. Astropack supports three types of printer interface: LPT1: - this is the standard, parallel connection used by most printers. COM1: - serial communication. If you use this, set the protocol from DOS using the MODE command. See the DOS manual for details. Disk - the program copies the table into a disk file. This is useful in a variety of situations. If your printer does not work with either of the previous interfaces, try using this and then printing the disk file later from MSDOS. You might also use this option if you do not actually want to print the table, but would like a stored copy on disk. When you select the third option from the Printer menu, the program will ask you for a filename. Be sure to give the name of a file that does not exist or is not valuable; any existing file would be overwritten. 10 A NOTE ON PRECISION: The sidereal time values that the program generates are accurate to within 1/10 of a second between the years 1930 to 2100. (Any values outside of these years from any function will probably be somewhat less accurate.) The results of the other functions should generally be treated as having three significant figures, even if the program gives more digits. Although some of the calculations are perhaps more precise, I prefer to err on the side of caution here.