Comet IRAS–Araki–Alcock (formal designation C/1983 H1, formerly 1983 VII) is a long-period

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

that, in 1983, made the closest known approach to Earth of any comet in 200 years, at a distance of about . The comet was named after its discoverers the

Infrared Astronomical Satellite The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mon ...

and two amateur

astronomers An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

George Alcock George Eric Deacon Alcock, MBE (28 August 1912, in Peterborough, Northamptonshire – 15 December 2000) was an English astronomer. He was one of the most successful visual discoverers of novae and comets. George’s interest in astronomy wa ...

of the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...

and Genichi Araki of

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. Both men were schoolteachers by profession, although Alcock was retired. Alcock had made his discovery simply by observing through the window of his home, using

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

."Obituary of George Alcock"

BBC News BBC News is an operational business division of the British Broadcasting Corporation (BBC) responsible for the gathering and broadcasting of news and current affairs in the UK and around the world. The department is the world's largest broadca ...

, 21 December 2000."Outbreak of Comet Fever"
''

Time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

'', 23 May 1983. "I've discovered a wonderful star ... Now I've got to discover a wonderful wife." During the closest approach, the comet appeared as a circular cloud about the size of the full moon, having no discernible tail, and shining at a naked eye

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

of 3–4. It swept across the sky at an angular speed of about 30 degrees per day. On May 11th the comet was detected on radar by

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science F ...

and

Goldstone Solar System Radar The Goldstone Solar System Radar (GSSR) is a large radar system used for investigating objects in the Solar System. Located in the desert near Barstow, California, it comprises a 500-kW X-band (8500 MHz) transmitter and a low-noise receiver on the ...

making it the first comet detected by two different radar systems. A second detection was made by Goldstone on 14 May. It is a long-period comet, with an orbital period of about 970 years, and is the parent comet of the minor Eta Lyrid

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extre ...

. This shower's radiant lies between

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, an ...

and Cygnus and produces 1 or 2 meteors an hour in mid-May with a peak between 9 May and 11 May.

Flyby comparison

Comet IRAS–Araki–Alcock made its closest approach to Earth in 1983, at a distance of about . It was the closest approach up to that time of any comet in 200 years; only

Lexell's Comet D/1770 L1, popularly known as Lexell's Comet after its orbit computer Anders Johan Lexell, was a comet discovered by astronomer Charles Messier in June 1770.Other comets named after their orbit computer, rather than discoverer, are 27P/Cromme ...

, in 1770, and 55P/Tempel-Tuttle, in 1366, are thought to have come closer. Subsequently, on 12 June 1999, the small comet P/1999 J6 (SOHO) passed about from Earth. What was thought to be a small fragment of 252P/LINEAR, called P/2016 BA14, passed at a distance of on 22 March 2016.

1983 Flyby

References

{{DEFAULTSORT:Iras-Araki-Alcock, 1983 H1 Near-Earth comets Non-periodic comets Discoveries by IRAS IRAS catalogue objects Astronomical objects discovered in 1983