International Comet Quarterly

Introduction to Comet C/2002 C1 (Ikeya-Zhang)

On 2002 Feb. 1, a comet was discovered visually by veteran comet hunter Kaoru Ikeya (Mori, Shuchi, Shizuoka, Japan) with a 25-cm-aperture reflector and a magnification of 39x, and by Daqing Zhang (near Kaifeng, Henan province, China) with a homemade 20-cm f/4.4 reflector at 28x. Zhang has been searching for comets for many years, but this is his first comet to carry his name. Ikeya has discovered four of the brightest comets of the past century, and this is his sixth comet, but his first comet discovery since 1967! The discovery was officially announced to the world on IAU Circular No. 7812.

During March and April 2002, comet C/2002 C1 was observable to northern-hemisphere observers low in the western sky about an hour after sunset for about 45 min in twilight before it set. It was then moving northward with respect to the stars, rapidly moving into the morning sky, soon visible all night long, and eventually southward again. It is now favorably placed for northern-hemisphere observers for many weeks (again in the evening sky in May and June) into the summer (and to southern-hemisphere observers since about mid-May 2002) as it slowly fades. It has been faintly visible to the naked eye from dark-sky sites in March, April, and even May, but for most observers (whether inexperienced comet observers or observers in light-polluted areas) the comet will largely be a binocular object until late May or June. Larger binoculars will be needed at this time, and it is expected to become a telescopic object in June/July 2002 as it recedes from the sun and earth. (These brightness predictions are based on typical comet behavior and could be off somewhat if the comet shows unusual brightness behavior.) During March and April, the comet showed an obvious tail even in small binoculars, but this tail shrank and faded rapidly as April progressed.

Comet C/2002 C1 is especially interesting because it appears to be a return of a fairly bright comet seen by Johannes Hevelius in February and March 1661. Hevelius was the premier comet observer in the mid-seventeenth century, and his astrometric measurements have allowed us (through orbital computations) to show that the comet designated C/1661 C1 is most likely the same as C/2002 C1 --- even though the observations from 1661 alone were not accurate enough to indicate that the comet had a 341-year period orbiting the sun (it has been merely assumed over the years that it was a long-period comet, with an orbit possibly in the thousands of years, though some people over the centuries have speculated on a link between C/1661 C1 and C/1532 R1 -- a link that now appears incorrect).

Some fabulous images of comet C/2002 C1 from photographs (copyrighted) taken by Michael Jaeger near Vienna, Austria, with a 30-cm-aperture f/3.3 deltagraph and a Schmidt camera (some Ektachrome, some Tech Pan photos):