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Halley's Comet

Halley's Comet or Comet Halley (/ˈhæli/ or /ˈheɪli/), officially designated 1P/Halley, is a short-period comet visible from Earth every 75–76 years. Halley is the only known 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. Halley last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061.

Halley's returns to the inner Solar System have been observed and recorded by astronomers since at least 240 BC. Clear records of the comet's appearances were made by Chinese, Babylonian, and medieval European chroniclers, but were not recognized as reappearances of the same object at the time. The comet's periodicity was first determined in 1705 by English astronomer Edmond Halley, after whom it is now named.

During its 1986 apparition, Halley's Comet became the first comet 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. These observations supported a number of longstanding hypotheses about comet construction, particularly Fred Whipple's "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 that substantially reformed and reconfigured these ideas; for instance, now it is understood that the surface of Halley is largely composed of dusty, non-volatile materials, and that only a small portion of it is icy.

C/2014 Q3

C/2014 Q3 (Borisov) is a periodic comet discovered at apparent magnitude 17 on 22 August 2014 by Gennady Borisov using a 0.3-meter (12 in) Astrograph. It is the third comet discovered by Borisov. The comet is best viewed from the northern hemisphere.

The comet was expected to reach about magnitude ~11 near perihelion (closest approach to the Sun), but has brightened to around magnitude 10. By 8 November 2014, the comet had a declination of +83 and was circumpolar from the northern hemisphere. The comet comes to perihelion on 19 November 2014 at a distance of 1.65 AU from the Sun.

Before entering the planetary region (epoch 1950), C/2014 Q3 had an orbital period of 148 years. After leaving the planetary region (epoch 2050), it will have an orbital period of 146 years.

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