In early 1985, Comet Halley will cross the orbit of Jupiter, and later that year the accelerating comet will pass the asteroid belt, the orbit of Mars, and arrive again for its once-in-a-human-lifetime visit to Earth (Figure 1). Obviously, this celestial event will be of enormous public interest: Ever since the ancient Chinese astronomers recorded their observations of Halley in 240 B.C., it has been a source of curiosity, awe, and fear. Swinging past the sun only once every 76 years, the comet has made the best of its brief moments in that vicinity by throwing out enormous amounts of gases and dust before returning to space.
Unlike its last appearance, in 1910, when the comet was easily seen, the 1985–1986 viewing will be unimpressive to the casual observer. The comet will be brightest during the first 3 weeks of February 1986, when it is nearest the sun (closest approach occurs February 9). Unfortunately, the comet will not be visible from the ground then because the earth will be on the other side of the sun. However, to observers, with binoculars, who find a location away from city lighting, Halley will be a rewarding sight in November and December 1985, and it will be at its best in March and early April 1986. Those equipped with a telescope will witness an even more impressive display.