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Halley's Comet


Halleys Comet
Digital Vision/ Photodisc/ Getty Images
Using Isaac Newton's new Laws of Motion, the astronomer, Edmond Halley, made a prediction in 1705. He stated that a comet which had appeared in 1531, 1607 and 1682 would reappear in 1758.

Although he was proven to be correct, Halley did not live to see it. However, the comet was later named in his honor.

During the 20th century, Halley's Comet appeared in 1910 and 1986. During that most recent visit, five spacecraft from the USSR, Japan, and the European Community journeyed to Comet Halley. ESA's Giotto obtained close-up photos of the nucleus of Halley's Comet. Because Halley is both large and active and has a well defined, regular orbit, it was a relatively easy target for Giotto and the other probes. However, it may not be representative of comets in general.

Halley's Comet played a prominent role in history because of its large nucleus and therefore great brightness and longevity. In 1066 when King Harold was overthrown by William the Conquerer at the Battle of Hastings, the cause of the event seems to have been pegged on a celestial visitor as is shown by the appearance of Halley's comet in the Bayeux Tapestry (left) which chronicles the event. In 1456, on a return passage, Halley's comet was excommunicated as an agent of the devil by Pope Calixtus III, but it didn't do any good - the comet has continued to return! During this same apparition, while Turkish forces were laying siege to Belgrade, the comet was described as a fearsome celestial apparition "with a long tail like that of a dragon" which was perceived by some as being in the form of "a long sword advancing from the west ... "

Although the average period of Halley's Comet's orbit is 76 years, it's not that easy to calculate the dates when it will return by simply subtracting multiples of 76 years from 1986. Gravity from other bodies in the solar system will affect its orbit. Over the centuries, Halley's orbital period has varied from 76 years to 79.3 years.

Comet Halley will return to the inner solar system in the year 2061, with a perihelion passage in early 2062.

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