Orwell Astronomical Society (Ipswich)

Home Events

Comet C/1983 H1 (IRAS-Araki-Alcock)

Comet C/1983 H1 (IRAS-Araki-Alcock) was first detected by the Infra-Red Astronomy Satellite (IRAS) on 25 April 1983 and found independently by the Japanese and English amateur astronomers, respectively Genich Araki and George Alcock, on 03 May 1983. It has a period of approximately 1000 years. Although small, the body passed Earth at a distance of only 4.6 million km on 11 May, making it an easy naked-eye object. It moved quickly through the sky and was visible for only seven nights.

The first observations by members of OASI were on 07 May during a meteor watch at Martin Cook's house. The observers used the ephemeris published by The Astronomer to locate the object in Draco. Initially, it appeared in binoculars as a diffuse, though surprisingly bright, blur. Late in the night, it was visible to the naked eye, but very faint.

On successive nights, the comet steadily brightened, becoming easily visible to the naked eye as a large, round, fuzzy patch with no apparent tail. A telescope showed a nucleus which was clearly asymmetric with respect to the surrounding diffuse material. As the comet brightened, it moved from Draco into Ursa Minor, Ursa Major and Cancer before becoming lost in the glow of sunset.

David Barnard