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Halley's Comet
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1P/Halley (Halley's Comet)
Discovery
Discovered by
prehistoric (observation);
Edmond Halley (recognition of periodicity)
Orbital characteristics
Epoch 2449400.5
(17 February 1994)
Aphelion
35.1 AU
(9 December 2023)
Perihelion
0.586 AU
last perihelion: 9 February 1986
next perihelion: 28 July 2061
17.8 AU
Eccentricity
0.967
75.3 a
Inclination
162.3°
Physical characteristics
Dimensions
15×8 km, 11 km (mean diameter)
Mass
2.2×1014 kg
0.6 (estimates range from 0.2 to 1.5 g/cm3)
~0.002 km/s
2.2 d (52.8 h) (?)
Albedo
0.04
28.2 (in 2003)
Halley's Comet or Comet Halley (/'hæli/ or /'he?li/), officially designated 1P/Halley, is the best-known of the short-period comets and is visible from Earth every 75–76 years. Halley is the only short-period comet that is clearly visible to the naked eye from Earth, and the only naked-eye comet that can appear twice in a human lifetime. Halley last appeared in the inner 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 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, 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.
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^ S. J. Peale (1989). "On the density of Halley's comet". Icarus 82 (1): 36–49. Bibcode:1989Icar...82...36P. doi:10.1016/0019-1035(89)90021-3. "densities obtained by this procedure are in reasonable agreement with intuitive expectations of densities near 1 g/cm3, the uncertainties in several parameters and assumptions expand the error bars so far as to make the constraints on the density uniformative ... suggestion that cometary nuclei tend to by very fluffy, ... should not yet be adopted as a paradigm of cometary physics."
^ S. J. Peale, J. J. Lissauer (1989). "Rotation of Halley's Comet". Icarus 79 (2): 396–430. Bibcode:1989Icar...79..396P. doi:10.1016/0019-1035(89)90085-7.
^ R. R. Britt (29 November 2001). "Comet Borrelly Puzzle: Darkest Object in the Solar System". Space.com. Retrieved 16 December 2008.
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^ G. W. Kronk. "1P/Halley". cometography.com. Retrieved 13 October 2008.
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^ O. Ajiki and R. Baalke. "Orbit Diagram (Java) of 1P/Halley". Jet Propulsion Laboratory Solar System Dynamics. Retrieved 1 August 2008.
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