Halleys Comet or Comet Halley (/ˈhæli/ or /ˈheɪli/), officially designated 1P/Halley,[2] is the best-known of the short-period comets and is visible from Earth every 75–76 years,[2][10] Halley is the only short-period comet that is clearly visible to the naked eye from Earth, and the only naked-eye comet that might appear twice in a human lifetime.[11] Other naked-eye comets may be brighter and more spectacular, but will appear only once in thousands of years. Halley last appeared in the inner Solar System in 1986 and will next appear in mid-2061.[12] Halleys returns to the inner Solar System have been observed and recorded by astronomers since at least 240 BC. Clear records of the comets appearances were made by Chinese, Babylonian, and medieval European chroniclers, but were not recognized as reappearances of the same object at the time. The comets periodicity was first determined in 1705 by English astronomer Edmond Halley, after whom it is now named. During its 1986 apparition, Halleys Comet became the first to be observed in detail by spacecraft, providing the first observational data on the structure of a comet nucleus and the mechanism of coma and tail formation.[13][14] These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipples dirty snowball model, which correctly predicted that Halley would be composed of a mixture of volatile ices – such as water, carbon dioxide and ammonia – and dust. The missions also provided data which substantially reformed and reconfigured these ideas; for instance it is now understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy
Posted on: Wed, 19 Mar 2014 14:07:14 +0000