|C/1983 H1 (IRAS-Araki-Alcock)|
Copyright © 1983 by Gary W. Kronk
Discovery [from Cometography - condense]
J. Davies and S. F. Green (University of Leicester), as well as B. Stewart (Rutherford Appleton Laboratory, England), were examining IRAS images on 1983 April 26, when they recognized a moving object on images obtained on April 25.85 and April 25.93, which represented two consecutive orbits. The object was thought to be a fast-moving minor planet and from the first image, Davies gave the position as α = 19h 07.6m, δ = +48° 43' (2000).
The Leicester group had formed a worldwide network of observatories to help in the confirmation of fast-moving objects, and telegrams were soon dispatched. T. Oja (Kvistaberg, Sweden) provided the first confirmation, but his three photographs obtained during April 27.89 to April 27.94 revealed a comet instead of a minor planet. The diameter of the nucleus was 15–20".
The initial request for observations sent out by the Leicester group did not include a message to the Central Bureau for Astronomical Telegrams (CBAT), the clearinghouse for comet information. CBAT did, however, know of the discovery through other sources. First, H. Rickman (Uppsala Observatory, Sweden) had left an unclear message on the bureau's answering machine, which did not give positions. Second, a conversation between B. G. Marsden (CBAT) and J. B. Gibson (Palomar Observatory, California, USA) took place on May 2, and the latter astronomer told Marsden that, at the request of a secondhand source, he had exposed several plates in the region of the supposed minor planet found by IRAS, but had not yet developed the plates.
Meanwhile, G. E. D. Alcock (Peterborough, England), a previous discoverer of four comets and four novae, had decided to conduct his routine nova search from inside his home on May 3. He was sweeping with 15 × 80 binoculars, through a closed window, when he located a large, diffuse object in Draco on May 3.92. Alcock quickly alerted several British amateur astronomers, one of which was G. S. Keitch, who, in turn, telephoned C. S. Morris (Cambridge, Massachusetts, USA). Morris then alerted CBAT. Shortly thereafter, on May 3.96, G. M. Hurst (Wellingborough, England), another British amateur alerted by Alcock, reported that he had confirmed the comet and determined its magnitude as 6.2. He added that the coma was 12' across.
CBAT now had two comet reports: Alcock's comet situated in Draco, and the IRAS object, for which they had no idea of its position in the sky. Marsden suspected these were the same. His suspicion was based on the facts that Alcock's comet was situated about 90° from the Sun and IRAS was restricted to only observing objects 90° from the Sun. Marsden telephoned Gibson, knowing he must have had positions to search for the "minor planet," and found out that the plates of May 2.46 and May 2.49 had revealed a comet. Gibson said the six-minute and four-minute exposures revealed trails, which exhibited a strongly condensed nucleus and a faint asymmetric coma about 2' across. The coma was denser on the northeast side, but no tail was visible.
The discovery saga did not end with Gibson's confirmation. While Marsden was trying to contact Davies to acquire the discovery observations, word came from Tokyo Observatory that G. Araki (Yuzawa, Niigata, Japan) had discovered a comet on May 3.61. He estimated the comet's magnitude as 7.
Prediscovery images were later found. T. Kumamori (Muro, Nara, Japan) found the comet on a photograph exposed on April 20.70, while the comet was found by H. Huth, P. Kroll, and G. Richter (Sonneberg Observatory, Germany) near the plate limit of two simultaneous exposures obtained on April 17.05. They estimated the magnitude as 12.