Halley’s Comet or Comet Halley is the best-known A _____ and is visible from Earth every 75 or 76 years. Halley is the only short-period comet that is clearly visible to the naked eye from the Earth, and thus the only naked-eye comet that B _____. Halley’s returns to the inner Solar System have been observed by astronomers C _____ , and recorded by Chinese, Babylonian and medieval European chroniclers, but were not recognized as reappearances of the same object. The comet’s periodicity was first determined in 1705 by English astronomer Edmond Halley, after whom it is now named. Halley’s Comet last appeared in the inner Solar System in 1986 and D _____.
During its 1986 apparition, Halley’s 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 E _____. These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple’s “dirty snowball” model, which correctly surmised that Halley would be composed of a mixture of volatile ices – such as water, carbon dioxide and ammonia – and dust. However, the missions also provided data F _____ , for instance, it is now understood that Halley’s surface is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy.
- of the short-period comets
- might appear twice in a human lifetime
- will next appear in mid-2061
- since at least 240 BC
- of coma and tail formation
- may be brighter and more spectacular
- which substantially reformed and reconfigured these ideas
| A | B | C | D | E | F |
