Solar system software
Early astronomers first looked at the obvious celestial bodies, the sun and the moon, before looking further. This was, in part, due to the limitations of the most common early astronomical tool: the human eye. In this section, we look at software that helps you look at the solar system.

Sun!
Ed Wilborne is the most prolific of the astronomical programmers, and we'll look at three of his programs. Sun! tells you the times of sunrise, sunset, transit (when the sun is due south, or local noon), and the beginning and end of three kinds of twilight, as shown in Figure A.

FIGURE A

Sun! provides a lot of information about the Sun's behavior in a small space!

As with all of Wilborne's programs, and most astronomical applications discussed here, you can set the date, time, and observing location. You'll need a couple of auxiliary applications to aid in the calculations, but Wilborne provides copies of these in his package. There is a version of Sun! available for a Windows desktop machine, too. Sun! is shareware; the fee is $5.

Moon!
This companion to Sun! gives you rise, set, and transit times, plus distance, for the moon. This application is slower than Sun! -- it takes the Palm computer nearly 20 seconds to grind through the math -- but the moon's orbit is complicated (it's the only body that ever gave Isaac Newton headaches when he tried to calculate its path). This is probably why the shareware fee for Moon! is $10.

J-Moons!
J-Moons! fills a special niche. If you're ever out at the telescope looking at Jupiter's four large moons, and a friend asks you which one is which, you can use this application to find out, as shown in Figure B. It will even flip the display over in case your telescope gives you a reversed view. The fee for J-Moons! is $5.

FIGURE B

J-Moons!' display shows you where the moons Callisto, Europa, Io, and Ganymede are for a chosen day and time.