On the nongravitational motion of Comet P/Halley

A method, based on the moments of perihelion passages used as observational data for the improvement of the orbital elements, is used to investigate the nongravitational motion of Comet P/Halley over a two millenia period. The nongravitational effects are examined as a secular change of the semimajor axis of the comet's orbit. By linking four or five consecutive perihelion times of the comet from the 87 B.C.-1986 A.D. interval, discrete values of the secular change of the semimajor axis are computed for 24 moments in that time interval. It is found that the simplest reasonable function of time for approximation of the nongravitational effects is a parabolic one. Using the 300 best selected positional observations from 1835-1987 and 25 perihelion times from 87 B.C.-1835 A.D., the comet's orbit was improved by including the nongravitational effects in the form of the parabolic function. A successful link is then made of all the observed appearances of the comet by one system of orbital elements.