A recent post and its accompanying link about the HP-40GS (thanks Woody Larkin) alerted me to the fact that a beautiful astronomy program has been written for the HP-39G (with variations for the 48 or 49), which turns this not very beautiful calculator into a wonderful tracker of the sun, moon, and planets.
The program (aplet), written by Khanh-Dang Nguyen Thu-Lam, is called HPlanetarium, and is available for download at Thu-Lam's website:
http://perso.wanadoo.fr/kdntl/hp49/hpl/index.en.html
For the sun, moon, and planets, HPlanetarium runs celestial circles around my 20-year-old program (Sky Map and Compass), which was written for the HP-41 with Navigation Pac. It is very easy to use, and displays times of rising and setting as well as current positions for the sun, moon, Mercury, Venus, Mars, Jupiter, and Saturn, as well as various other information such as the phase of the moon and the positions of Jupiter's four biggest planets. It does not display, however, the coordinates of the 58 navigational stars that are included in the 41 Navigational Pac, and hence is not intended so much for navigation.
Thu-Lam's program reminds me of Eric Burgess' Celestial BASIC, which was written for a PC. It is beautiful to see this mini version run on the lowly 39G. I had almost given up on ever using my 39G, but now it has found a new life.
Cheers, Tom