Halleys comet

Halley's comet or Comet Halley , periodic comet named for Edmond Halley, who observed it in 1682 and identified it as the one observed in 1531 and 1607. Halley did not live to see its return in 1758, close to the time he predicted. It reappeared in 1835 when it was carefully recorded by visual observers, and in 1910, when its long tail and outbursts of dust jets were observed photographically. For its most recent return in 1985 and 1986, astronomers observed it from the ground and from space. A massive observing effort (1982-89) including visual observations, photography, and studies of the area around the nucleus, was coordinated by the International Halley Watch. Japan, the European Space Agency, and the USSR sent spacecraft to study the comet; the Vega and Giotto probes revealed a darker-than-expected nucleus 8 km (5 mi) wide and 15 km (9 mi) long, and shaped like a potato.

Bibliography: See NASA Special Publications, Atlas of Comet Halley (1987); M. Grewing, ed., Exploration of Halley's Comet (1988).

Halley's Comet a periodical comet with an orbital period of about 76 years, its reappearance in 1758–9 having been predicted by the English astronomer and mathematician Edmond Halley (1656–1742), who identified it. It was first recorded in 240 bc and last appeared, rather faintly, in 1985–6, when the European space probe Giotto took close-up photographs of the nucleus.