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.
SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 51.4 kiloparsecs from Earth and was the closest observed supernova since Kepler's Supernova in 1604. Light and neutrinos from the explosion reached Earth on February 23, 1987 and was designated "SN 1987A" as the first supernova discovered that year. Its brightness peaked in May of that year, with an apparent magnitude of about 3.
Halley's Comet is the only known short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years. It last appeared in the inner parts of the Solar System in 1986 and will next appear in mid-2061. Officially designated 1P/Halley, it is also commonly called Comet Halley, or sometimes simply Halley.
The Solar and Heliospheric Observatory (SOHO) is a European Space Agency (ESA) spacecraft built by a European industrial consortium led by Matra Marconi Space that was launched on a Lockheed Martin Atlas IIAS launch vehicle on 2 December 1995, to study the Sun. It has also discovered over 5,000 comets. It began normal operations in May 1996. It is a joint project between the European Space Agency (ESA) and NASA. SOHO was part of the International Solar Terrestrial Physics Program (ISTP). Originally planned as a two-year mission, SOHO continues to operate after almost 29 years in space; the mission has been extended until the end of 2025, subject to review and confirmation by ESA's Science Programme Committee.
Rashid Alievich Sunyaev is a German, Soviet, and Russian astrophysicist of Tatar descent. He got his MS degree from the Moscow Institute of Physics and Technology (MIPT) in 1966. He became a professor at MIPT in 1974. Sunyaev was the head of the High Energy Astrophysics Department of the Russian Academy of Sciences, and has been chief scientist of the Academy's Space Research Institute since 1992. He has also been a director of the Max Planck Institute for Astrophysics in Garching, Germany since 1996, and Maureen and John Hendricks Distinguished Visiting Professor in the School of Natural Sciences at the Institute for Advanced Study in Princeton since 2010. In February 2022, he signed an open letter from Russian scientists and science journalists condemning Russia's invasion of Ukraine.
The coma is the nebulous envelope around the nucleus of a comet, formed when the comet passes near the Sun in its highly elliptical orbit. As the comet warms, parts of it sublimate; this gives a comet a diffuse appearance when viewed through telescopes and distinguishes it from stars. The word coma comes from the Greek κόμη (kómē), which means "hair" and is the origin of the word comet itself.
The Orbiting Astronomical Observatory (OAO) satellites were a series of four American space observatories launched by NASA between 1966 and 1972, managed by NASA Chief of Astronomy Nancy Grace Roman. These observatories, including the first successful space telescope, provided the first high-quality observations of many objects in ultraviolet light. Although two OAO missions were failures, the success of the other two increased awareness within the astronomical community of the benefits of space-based observations, and led to the instigation of the Hubble Space Telescope.
International Ultraviolet Explorer, was the first space observatory primarily designed to take ultraviolet (UV) electromagnetic spectrum. The satellite was a collaborative project between NASA, the United Kingdom's Science and Engineering Research Council and the European Space Agency (ESA), formerly European Space Research Organisation (ESRO). The mission was first proposed in early 1964, by a group of scientists in the United Kingdom, and was launched on 26 January 1978, 17:36:00 UTC aboard a NASA Thor-Delta 2914 launch vehicle. The mission lifetime was initially set for 3 years, but in the end, it lasted 18 years, with the satellite being shut down in 1996. The switch-off occurred for financial reasons, while the telescope was still functioning at near original efficiency.
Comet dust refers to cosmic dust that originates from a comet. Comet dust can provide clues to comets' origin. When the Earth passes through a comet dust trail, it can produce a meteor shower.
The nucleus is the solid, central part of a comet, formerly termed a dirty snowball or an icy dirtball. A cometary nucleus is composed of rock, dust, and frozen gases. When heated by the Sun, the gases sublime and produce an atmosphere surrounding the nucleus known as the coma. The force exerted on the coma by the Sun's radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. A typical comet nucleus has an albedo of 0.04. This is blacker than coal, and may be caused by a covering of dust.
Comet Bennett, formally known as C/1969 Y1, was one of the two bright comets observed in the 1970s, along with Comet West and is considered a great comet. The name is also borne by an altogether different comet, C/1974 V2. Discovered by John Caister Bennett on December 28, 1969, while still almost two AUs from the Sun, it reached perihelion on March 20, passing closest to Earth on March 26, 1970, as it receded, peaking at magnitude 0. It was last observed on February 27, 1971.
The International Astrophysical Observatory "GRANAT", was a Soviet space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations. It operated for almost nine years.
Spektr-R was a Russian scientific satellite with a 10 m (33 ft) radio telescope on board. It was launched on 18 July 2011 on a Zenit-3F launcher from Baikonur Cosmodrome, and was designed to perform research on the structure and dynamics of radio sources within and beyond the Milky Way. Together with some of the largest ground-based radio telescopes, the Spektr-R formed interferometric baselines extending up to 350,000 km (220,000 mi).
Gamma-ray astronomy is a subfield of astronomy where scientists observe and study celestial objects and phenomena in outer space which emit cosmic electromagnetic radiation in the form of gamma rays, i.e. photons with the highest energies at the very shortest wavelengths. Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy.
A comet tail and coma are visible features of a comet when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.
The Orbiting Astronomical Observatory 2 was the first successful space telescope, launched on December 7, 1968. An Atlas-Centaur rocket launched it into a nearly circular 750-kilometre (470 mi) altitude Earth orbit. Data was collected in ultraviolet on many sources including comets, planets, and galaxies. It had two major instrument sets facing in opposite directions; the Smithsonian Astrophysical Observatory (SAO) and the Wisconsin Experiment Package (WEP). One discovery was large halos of hydrogen gas around comets, and it also observed Nova Serpentis, which was a nova discovered in 1970.
Alexandr Boyarchuk was a Russian physicist and astronomer.
