Astronomer's Pal
Version 0.1

By Luke Haywas, United States Air Force Academy

C05luke.haywas@usafa.af.mil

This program is distributed free of charge under the following conditions:

-	it must be distributed in a complete copy of the original archive;
-	the program and source code may not be modified or redistributed;
-	the author must be credited for the work.

The source code is included so that you can take a look at the mathematical algorithms that make up the calculations. Please feel free to use the math for your own purposes, but do not modify or recompile the original code, or use portions of the code in your own work.

Astronomer's Pal is a simple program for the TI-89 which will be of use for amateur astronomers. It may run on the TI-92 as well but I have not tested it; I suspect in such a case it will not make full use of the available screen area. Tested on a HW1 TI-89 with AMS 2.08, so it should work fine on all 2.xx versions.

It is written in GCC and runs without any kernel. Unlike the TI-BASIC programs I released a while ago, this program works correctly, giving you the right answers. As far as I have tested.

This program will ask for your latitude and longitude (easy to find on the internet these days) as well as the local date and time. Also enter your time zone.

IMPORTANT!!!  Times must be in 24-hour format, i.e. 6 PM is 1800. Latitude and longitude are in degrees, and WEST longitude or SOUTH latitude is NEGATIVE. Enter hour and minute separately. Also, when entering your local time, use STANDARD time. If you are on daylight saving time, make sure you correct it to standard, otherwise the error going into your calculations will be 15 degrees and this propagates with each calculation!

The program WILL NOT WORK if you wish to use dates in the past, i.e. before 1 January 2000. Additionally, after 2100, there will be a 4 minute error in the sidereal time calculation, and this will again increase by 4 minutes every century thereafter. Again, this error propagates with each calculation.

The program will then prompt you for the celestial coordinates - right ascension and declination -  of the object you wish to observe. Enter them in degrees.

The display will include local and Zulu (Greenwich Mean) time and date, your local sidereal time, your position on the globe, the right ascension and declination of the object you wish to look at, and then the most useful numbers, the AZIMUTH and ELEVATION at which you will find the object of interest. Point your telescope in these directions. Azimuth 0 is due north. Elevation 0 is on the horizon; 90 is at the zenith. Note that if the program returns a negative elevation, the object is below the horizon, and has either already set, or not yet risen. Also, it may just be that its declination is such that you may never see it from your particular latitude. (for example, observers in the northern hemisphere cannot ever see Alpha Centauri, and those in the southern cannot see Polaris.)

Please note that this program is NOT idiot-proof! There are NO checks to make sure that you have entered valid numbers, so if you do not put a number in the correct range in every value, the program WILL CRASH! I GUARANTEE that it will. So use at your own risk. Obviously, I assume zero responsibility for any damage that the program may cause to anything.

Enjoy this program; I hope you find it useful. Please email me with errors or suggestions.

			Regards,
				Cadet Luke Haywas
				US Air Force Academy

Future updates:

-	user-friendly (idiot proof) input interface
-	ability to update only time and RA/DEC so you don't waste time inputting redundant values
-	ability to preset latitude, longitude, and time zone (will also include all the time zones) and select from a list
-	library of the most popular celestial body coordinates for easy calculation
-	Moon and Planets calculation algorithms

Version History
0.1	20 November 2002			 First public release/beta 1
