Comet IRAS–Araki–Alcock

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Comet IRAS–Araki–Alcock
11 May 1983 ~06:00 UT
Orbital characteristics[1]
Epoch 13 May 1983 (JD 2445467.5)
Aphelion195.052477±0.42817 AU[1]
Perihelion0.99134097 ± 2.876×10−7 AU
98.021909±0.21517 AU
970.49 years
Earth MOID0.00583 AU (872000 km; 542000 mi)
Physical characteristics
Dimensions9.2 km in diameter[2]
A false colour image of Comet IRAS–Araki–Alcock in 1983, viewed in infrared light by the Infrared Astronomical Satellite (IRAS)
This figure combines an International Ultraviolet Explorer FES image showing its diffuse tail, and the long-wavelength redundant (LWR) spectrum depicting the molecular emission lines of sulfur (S2) and hydroxyl (OH).

Comet IRAS–Araki–Alcock (formal designation C/1983 H1, formerly 1983 VII) is a long-period comet that, in 1983, made the closest known approach to Earth of any comet in 200 years, at a distance of about 0.0312 AU (4,670,000 km; 2,900,000 mi). The comet was named after its discoverers – the Infrared Astronomical Satellite and two amateur astronomers, George Alcock of the United Kingdom and Genichi Araki of Japan. 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.[3][4] 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 of 3–4. It swept across the sky at an angular speed of about 30 degrees per day. On May 11 the comet was detected on radar by Arecibo Observatory and Goldstone Solar System Radar making it the first comet detected by two different radar systems.[5] A second detection was made by Goldstone on 14 May.[5]

It is a long-period comet, with an orbital period of about 970 years,[1] and is the parent comet of the minor Eta Lyrid meteor shower.[6] This shower's radiant lies between Vega and Cygnus and produces 1 or 2 meteors an hour in mid-May with a peak between 9 May and 11 May.

Flyby comparison[edit]

Comet IRAS–Araki–Alcock made its closest approach to Earth in 1983, at a distance of about 0.0312 AU (4,670,000 km; 2,900,000 mi). It was the closest approach up to that time of any comet in 200 years; only Lexell's Comet, in 1770, and 55P/Tempel-Tuttle, in 1366, are thought to have come closer.[7][8] Subsequently, on 12 June 1999, the small comet P/1999 J6 (SOHO) passed about 0.012 AU (1,800,000 km; 1,100,000 mi) from Earth.[9] What was thought to be a small fragment of 252P/LINEAR, called P/2016 BA14, passed at a distance of 0.0237 AU (3,550,000 km; 2,200,000 mi) on 22 March 2016.[10]

1983 Flyby[edit]

The comet passed from north to south between 9 May to 13 May, passing through Ursa Major towards Cancer. Its motion is marked every 2 hours here.

Moving north to south, it crossed just inside the earth's orbit on 11 May.


  1. ^ a b c "JPL Orbital Elements: C/1983 H1 (IRAS-Araki-Alcock)". Retrieved 7 April 2020. 1983-10-04 last obs (arc=160 days)
  2. ^ a b c "JPL Orbital Elements: C/1983 H1 (IRAS-Araki-Alcock)". Retrieved 28 June 2012. 1983-10-04 last obs (arc=160 days)
  3. ^ "Obituary of George Alcock", BBC News, 21 December 2000.
  4. ^ "Outbreak of Comet Fever", Time, 23 May 1983. "I've discovered a wonderful star ... Now I've got to discover a wonderful wife."
  5. ^ a b Harmon, J.K; Campbell, D.B; Ostro, S.J; Nolan, M.C (1999). "Radar observations of comets" (PDF). Planetary and Space Science. 47: 1409–1422. doi:10.1016/S0032-0633(99)00068-9. Retrieved 22 November 2020.
  6. ^ "Eta Lyrids". Meteor Showers Online. Archived from the original on 5 May 2012. Retrieved 21 November 2008.
  7. ^ "Closest Approaches to the Earth by Comets". Minor Planet Center. Retrieved 28 June 2012.
  8. ^ "JPL Close-Approach Data: C/1983 H1 (IRAS-Araki-Alcock)". Retrieved 28 June 2012. 1983-10-04 last obs (arc=160 days)
  9. ^ "JPL Close-Approach Data: P/1999 J6 (SOHO)". Retrieved 28 June 2012. 2010-04-22 last obs (arc=10.9 yr; JFC)
  10. ^ "NEO Earth Close Approaches". Archived from the original on 7 March 2014. Retrieved 4 March 2014.