Originally from ticket #27029.
By the way, no big deal and I'm not complaining, but the Halley's comet position from March 22 through April 5, 1986, appears to be off. Sky and Telescope charts along with some photos I took during that time seem to confirm this. The comet was moving from Sagittarius through Scorpius. My March 22 photos show Halley's west of the Sagittarius "teapot". On April 4 and 5, my photos and Sky and Telescope's sky maps show it below Scorpius and in Norma. Sky Safari has Halley too far west in Centaurus. I guess I'm too picky! Oh well, if nothing else, this has brought back some great memories when I dug up these old pictures. Thank you for a great program and allowing me to travel back in time.
Bill Tschumy replies;
With respect to Halley's Comet. Comets are perturbed by other solar system bodies and thus don't follow true Keplerian orbits. For plotting the positions of comets we take the current orbital elements from the Minor Planet Center and plot its position based upon that. However this doesn't work well when extrapolating back to other apparitions of the comet. To do so we would need the orbital elements from 1986 and we don't have those built into SkySafari (not are they easily automatically downloaded).