Halley's Comet (redirected from Haley's Comet)

Halley's comet or Comet Halley (hăl`ē, hā`lē), 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).

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Halley's Comet

 or Comet Halley

First comet whose return was predicted, proving that at least some comets are members of the solar system. Edmond Halley showed in 1705 that comets seen in 1531, 1607, and 1682 were really one comet, and he predicted its return in 1758. Later calculations identified it with the large, bright comet seen during the Norman Conquest (and depicted in the Bayeux Tapestry) and with other comet sightings at intervals of about 76 years, the first in 240 BC. The only easily seen comet that returns in a single lifetime, it approached Earth twice in the 20th century (1910, 1985–86). Its nucleus is roughly 9 mi (15 km) across.

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Halley's Comet [′hal·ēz ¦käm·ət]

(astronomy)

A member of the solar system, with an orbit and a period of about 76 years; its nucleus is about 9 miles (15 kilometers) in diameter; next due to appear in 2061. Also known as Comet Halley.

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Halley’s Comet 

a bright comet, the first for which an elliptic orbit was calculated, thereby proving the periodicity of its return to the sun. The English astronomer E. Halley, who compiled the first catalog of the elements of the orbits of comets that appeared between 1337 and 1698, noted the coincidence of the paths of the comets of 1531, 1607, and 1682 and proposed that they corresponded to one and the same comet that revolved around the sun with a period of 75-76 years. In 1705, Halley predicted the return of the comet in 1758. In 1758 the French scientist A. Clairaut developed a method of accounting for the perturbations of the comet’s motion caused by the attraction of the planets Jupiter and Saturn and refined the estimate of the date of the comet’s passage through the perihelion. It occurred on Mar. 12, 1759, within the probable period of time indicated by Clairaut. This was a brilliant confirmation of Newton’s mechanics. The perihelion of the orbit of Halley’s comet is 0.587 astronomical unit and the aphelion, more than 35 astronomical units. The next passage of the comet was in 1835. By this time, the perturbations in the comet’s motion by the planet Uranus, which was recently discovered by the English astronomer W. Herschel were also taken into account. The comet passed through the perihelion on November 16, three days later than calculated. The study of Halley’s comet by the German astronomer F. W. Bessel marked the beginning of the mechanical theory of comet forms, later continued by the Russian astronomer F. A. Bredikhin. Investigations of Halley’s comet during its last appearance (perihelion May 19, 1910), based on numerous observations, made it possible to obtain the first information on the physical nature of comets and stimulated P. Cowell to develop a more complete method of calculating perturbations by planets. Together with A. Crommelin, he traced the future motion of Halley’s comet as well as its past motion. It has turned out that up to 1909, Halley’s comet was observed 29 times, for the first time in A.D. 446. The next passage of Halley’s comet through the perihelion will occur in January 1986. This will afford one of the most convenient opportunities in the second half of the 20th century for sending a probe-rocket to a comet with the aim of directly determining the composition of comets and the state of matter within them.

REFERENCE

Orlov, S. V. O prirode komet. Moscow, 1958.

O. V. DOBROVOL’SKII