A comet is an icy, small Solar System body that warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or coma surrounding the nucleus, and sometimes a tail of gas and dust gas blown out from the coma. These phenomena are due to the effects of solar radiation and the outstreaming solar wind plasma 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 close and bright, a comet may be seen from Earth without the aid of a telescope and can subtend an arc of up to 30° across the sky. Comets have been observed and recorded since ancient times by many cultures and religions.
Comet Hyakutake is a comet discovered on 31 January 1996. It was dubbed the Great Comet of 1996; its passage to within 0.1 AU (15 Gm) of the Earth on 25 March was one of the closest cometary approaches of the previous 200 years. Reaching an apparent visual magnitude of zero and spanning nearly 80°, Hyakutake appeared very bright in the night sky and was widely seen around the world. The comet temporarily upstaged the much anticipated Comet Hale–Bopp, which was approaching the inner Solar System at the time.
Comet Ikeya–Seki, formally designated C/1965 S1, 1965 VIII, and 1965f, was a long-period comet discovered independently by Kaoru Ikeya and Tsutomu Seki. First observed as a faint telescopic object on September 18, 1965, the first calculations of its orbit suggested that on October 21, it would pass just 450,000 km (280,000 mi) above the Sun's surface, and would probably become extremely bright.
Comet West, formally designated C/1975 V1, 1976 VI, and 1975n, was a comet described as one of the brightest objects to pass through the inner Solar System in 1976. It is often described as a "great comet."
The Kreutz sungrazers are a family of sungrazing comets, characterized by orbits taking them extremely close to the Sun at perihelion. At the far extreme of their orbits, aphelion, Kreutz sungrazers can be a hundred times farther from the Sun than the Earth is, while their distance of closest approach can be less than twice the Sun's radius. They are believed to be fragments of one large comet that broke up several centuries ago and are named for German astronomer Heinrich Kreutz, who first demonstrated that they were related. These sungrazers make their way from the distant outer Solar System to the inner Solar System, to their perihelion point near the Sun, and then leave the inner Solar System in their return trip to their aphelion.
The Solar Orbiter (SolO) is a Sun-observing probe developed by the European Space Agency (ESA) with a National Aeronautics and Space Administration (NASA) contribution. Solar Orbiter, designed to obtain detailed measurements of the inner heliosphere and the nascent solar wind, will also perform close observations of the polar regions of the Sun which is difficult to do from Earth. These observations are important in investigating how the Sun creates and controls its heliosphere.
Comet Skorichenko–George is also designated C/1989 Y1, 1990 VI, and 1989e1. It was discovered on December 17, 1989 by Doug George of Kanata, Ontario, Canada, and Soviet astronomer Boris Skoritchenko. Skoritchenko was using 8×20 binoculars, whilst George was using a 16" reflector and had searched for 65 hours. The comet was magnitude 10.5 in the northern evening sky. It passed its perihelion on April 11, 1990 at a distant 1.57 AU, and remained in the Earth's evening sky through April 1990, at magnitude 9–10.
Comet 96P/Machholz or 96P/Machholz 1 is a short-period sungrazing comet discovered on May 12, 1986, by amateur astronomer Donald Machholz on Loma Prieta peak, in central California using 130 millimetres (5.1 in) binoculars. On June 6, 1986, 96P/Machholz passed 0.404 AU from the Earth. 96P/Machholz last came to perihelion on January 31, 2023. The comet has an estimated diameter of around 6.4 km (4.0 mi).
Comet C/1993 Y1 (McNaught–Russell) is a long (time) period comet that reached a maximum magnitude of 6.5 in early 1994. It was discovered by Robert H. McNaught and Kenneth S. Russell using the U.K. Schmidt Telescope in Australia. McNaught and Russell worked at Siding Spring Observatory and together discovered five comets between 1991 and 1995.
An antitail is an apparent spike projecting from a comet's coma which seems to go towards the Sun, and thus geometrically opposite to the other tails: the ion tail and the dust tail. Despite a common misunderstanding, this phenomenon is not an optical illusion. The antitail consists of larger dust particles left behind by the comet. These dust particles are less affected by the Sun's radiation pressure and tend to remain roughly in the comet's orbital plane and eventually form a disc along the comet's orbit due to the ejection speed of the particles from the comet's surface. As Earth passes through the comet's orbital plane, this disc is seen side on, and appears as the characteristic spike. The other side of the disc can sometimes be seen, though it tends to be lost in the dust tail. The antitail is therefore normally visible for a brief interval only when Earth passes through the comet's orbital plane.
The Great Comet of 1823, also designated C/1823 Y1 or Comet De Bréauté-Pons, was a bright comet visible in the last month of 1823 and the first months of 1824.
76P/West–Kohoutek–Ikemura is a Jupiter-family periodic comet in the Solar System with a current orbital period of 6.48 years.
C/2018 Y1 (Iwamoto) is a long period comet with a retrograde orbit discovered on December 18, 2018, by Japanese amateur astronomer Masayuki Iwamoto. Its period is estimated to be 1,733 years. It passed closest to Earth on February 13, 2019. It was expected to reach a magnitude of between 6.5 and 7.5, visible in binoculars or a small telescope and was reported to reach a magnitude of 5.5 by Juan Jose Gonzalez on February 13, before fading to 7.6 two weeks later.
C/2019 Y4 (ATLAS) was a comet with a near-parabolic orbit discovered by the ATLAS survey on December 28, 2019. Early predictions based on the brightening rate suggested that the comet could become as bright as magnitude 0 matching the brightness of Vega. It received widespread media coverage due to its dramatic increase in brightness and orbit similar to the Great Comet of 1844, but on March 22, 2020, the comet started disintegrating. Such fragmentation events are very common for Kreutz Sungrazers. The comet continues to fade and did not reach naked eye visibility. By mid-May, comet ATLAS appeared very diffuse even in a telescope. C/2019 Y4 (ATLAS) has not been seen since May 21, 2020.
C/2020 F3 (NEOWISE) or Comet NEOWISE is a long period comet with a near-parabolic orbit discovered on March 27, 2020, by astronomers during the NEOWISE mission of the Wide-field Infrared Survey Explorer (WISE) space telescope. At that time, it was an 18th-magnitude object, located 2 AU away from the Sun and 1.7 AU away from Earth.
C/2020 F8 (SWAN), or Comet SWAN, is an Oort cloud comet that was discovered in images taken by the Solar Wind Anisotropies (SWAN) camera on March 25, 2020, aboard the Solar Heliospheric Observer (SOHO) spacecraft. In the glare of twilight, Comet SWAN is difficult to find with 50mm binoculars even though it is still near the theoretical range of naked eye visibility. The comet has dimmed since May 3. As of perihelion, the comet is very diffuse, does not have a visible nucleus and is not a comet that will be noticed by inexperienced observers. It is likely that the comet disintegrated.
C/2017 T2 (PanSTARRS) is an Oort cloud comet discovered on 2 October 2017 when it was 9.2 AU (1.38 billion km) from the Sun. The closest approach to Earth was on 28 December 2019 at a distance of 1.52 AU (227 million km). It came to perihelion on 4 May 2020 when it was safe from disintegration at 1.6 AU from the Sun.
C/2022 E3 (ZTF) is a non-periodic comet from the Oort cloud that was discovered by the Zwicky Transient Facility (ZTF) on 2 March 2022. The comet has a bright green glow around its nucleus, due to the effect of sunlight on diatomic carbon and cyanogen. The comet's systematic designation starts with C to indicate that it is not a periodic comet, and "2022 E3" means that it was the third comet to be discovered in the first half of March 2022.
C/2023 V5 (Leonard) was discovered on 6 November 2023 by the Catalina Sky Survey. It came to perihelion on 13 December 2023 at 0.849 AU (127.0 million km), from the Sun. It is probably a Liller family comet, together with C/1988 A1 (Liller), C/1996 Q1 (Tabur), C/2015 F3 (SWAN), and C/2019 Y1 (ATLAS).
