On the motion of Comet Halley

Results of orbit determinations of Comet Halley are discussed, and it is suggested that a radial light offset can be eliminated by using from the observations only the position angles relative to the sun. It is shown that the Rickman and Froeschle (1982) models for the nongravitational forces on Comet Halley may be more accurate than the model of Delsemme (1982). Results are given for discrete solutions for the nongravitational forces at different parts of the orbit to improve the models through determination of quantities such as lag angle at different distances and orientation of the spin axis. It is suggested that the nongravitational forces on the comet increase by about 0.5 percent per revolution. The perihelion time in 837 AD is calculated precisely from that of earlier apparitions, and an integration of the motion of the comet for 467 BC to 2580 AD is presented.