Comet IRAS–Araki–Alcock

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Comet IRAS–Araki–Alcock
Comet IRAS-Araki-Alcock by Russell E Milton.jpg
May 11, 1983 ~6 UT
Orbital characteristics[1]
Epoch 1983-May-13 (2445467.5)
Aphelion 195.0524769[1]
Perihelion 0.9913410
Eccentricity 0.9898865
970.49 years
Inclination 73.2513669
Earth MOID 0.00583 AU (872,000 km; 542,000 mi)
Physical characteristics
Dimensions 9.2 km in diameter[2]
Albedo 0.02[2]

Comet IRAS–Araki–Alcock (formal designation C/1983 H1, formerly 1983 VII) is a long-period comet that, in 1983, made the closest approach to Earth, about 0.0312 AU (4,670,000 km; 2,900,000 mi), of any comet in 200 years; only Lexell's Comet, in 1770, and 55P/Tempel-Tuttle, in 1366, are thought to have come closer.[3][4] (The small comet P/1999 J6 (SOHO) passed about 0.012 AU (1,800,000 km; 1,100,000 mi) from Earth on 1999-Jun-12.[5] and 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[6])

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).

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.[7][8]

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 incredible speed of some 30 degrees per day.

IRAS-Araki-Alcock 1983 starmap.png
The comet passed from north to south between May 9 to 13, passing through Ursa Major towards Cancer. Its motion is marked every 2 hours here.
IRAS-Araki-Alcock 1983 orbit near-earth.png
Moving north to south, it crossed just inside the earth's orbit on May 11.

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


  1. ^ a b c "JPL Orbital Elements: C/1983 H1 (IRAS-Araki-Alcock)" (1983-10-04 last obs (arc=160 days)). Retrieved 2012-06-28. 
  2. ^ a b c "JPL Orbital Elements: C/1983 H1 (IRAS-Araki-Alcock)" (1983-10-04 last obs (arc=160 days)). Retrieved 2012-06-28. 
  3. ^ "Closest Approaches to the Earth by Comets". Minor Planet Center. Retrieved 2012-06-28. 
  4. ^ "JPL Close-Approach Data: C/1983 H1 (IRAS-Araki-Alcock)" (1983-10-04 last obs (arc=160 days)). Retrieved 2012-06-28. 
  5. ^ "JPL Close-Approach Data: P/1999 J6 (SOHO)" (2010-04-22 last obs (arc=10.9 yr; JFC)). Retrieved 2012-06-28. 
  6. ^ "Archived copy". Archived from the original on March 7, 2014. Retrieved March 4, 2014. 
  7. ^ 'Obituary of George Alcock' BBC News, 21-12/2000
  8. ^ 'Outbreak of Comet Fever', TIME Magazine, 23-05-83. "I've discovered a wonderful star," commented Araki, "Now I've got to discover a wonderful wife."
  9. ^ 'Eta Lyrids', Meteor Showers Online, accessed 21-11-08