page_title: Comet
section_title: Nomenclature
hierarchical_section_title: Comet / Nomenclature
caption_attribution_description: An image of Halley's Comet taken June 6, 1910.
context_page_description: A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are due to the effects of solar radiation and the solar wind acting upon the nucleus of the comet. Comet nuclei range from a few hundred meters to tens of kilometers across and are composed of loose collections of ice, dust, and small rocky particles. The coma may be up to 15 times Earth's diameter, while the tail may stretch beyond one astronomical unit. If sufficiently bright, a comet may be seen from Earth without the aid of a telescope and may subtend an arc of 30° across the sky. Comets have been observed and recorded since ancient times by many cultures.
  Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune.
context_section_description: The names given to comets have followed several different conventions over the past two centuries. Prior to the early 20th century, most comets were simply referred to by the year when they appeared, sometimes with additional adjectives for particularly bright comets; thus, the "Great Comet of 1680", the "Great Comet of 1882", and the "Great January Comet of 1910".
  After Edmund Halley demonstrated that the comets of 1531, 1607, and 1682 were the same body and successfully predicted its return in 1759 by calculating its orbit, that comet became known as Halley's Comet. Similarly, the second and third known periodic comets, Encke's Comet and Biela's Comet, were named after the astronomers who calculated their orbits rather than their original discoverers. Later, periodic comets were usually named after their discoverers, but comets that had appeared only once continued to be referred to by the year of their appearance.
  In the early 20th century, the convention of naming comets after their discoverers became common, and this remains so today. A comet can be named after its discoverers, or an instrument or program that helped to find it. For example, in 2019, astronomer Gennady Borisov observed a comet that appeared to have originated outside of the solar system, the comet was named C/2019 Q4 (Borisov) after him.
caption: Halley's Comet in 1910
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