Rotational period of comet Halley

Abstract

The rotational period of the nucleus of comet Halley is a basic datum which must be accurately known if the vast collection of observations of this comet recently obtained from spacecraft and ground-based observatories are to be correctly interpreted. Sekanina and Larson, who have studied the morphology of the comet's coma, find a period near 2.2 days, as do investigators associated with the Planet-A, Vega 1 and Vega 2 imaging experiments^1-4. Others, however, have reported significantly different values, or have been unable to find clear evidence of periodicity in their data^5-7. We report here the results of ground-based photometry of comet Halley carried out during March and April 1986 which indicate that the rotational period of the comet is, in fact, near 7.4 days.