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COMET C/2000 WM1 (LINEAR)

Discovery:

Shortly after mid-December of 2000, the LINEAR team announced the discovery of an asteroidal object on images obtained on December 16.07. The magnitude was given as 17.8. The available positions allowed the Central Bureau for Astronomical Telegrams (the clearinghouse for observations of comets and asteroids) to determine a rough orbit, which, in turn, allowed them to link these observations to another LINEAR object detected on November 16 and 18. Interestingly, T. B. Spahr (Smithsonian Astrophysical Observatory, Mt. Hopkins) observed the object on December 20.15 and detected a coma 10 arcsec across and a broad, faint tail extending 10-20 arcsec toward PA 45°. Thus, the object was really a comet.

Following the recognition that this object was a comet, Brian G. Marsden (Central Bureau) calculated a parabolic orbit which indicated the comet would pass only 0.55 AU from the sun on 2002 January 22.78. This early orbit indicated the comet might reach a maximum brightness of magnitude 4.

The comet began brightening more rapidly in November. It began the month at magnitude 9.5 and ended the month slightly brighter than magnitude 6. Interestingly, the comet began brightening faster than expected during the latter half of November, but it is not known how long this trend will continue. Some unusual features were also becoming visible. Michael Jäger of Austria photographed a very narrow anti-tail on November 16 (see below). Other observers began detecting it during the next few days. Giovanni Sostero (Italy) was observing with an 8-inch Schmidt-Cassegrain on the 16th and "caught a structure similar to a 'jet'." He said it was 0.6 arcmin long and extended toward PA 145°.

The comet moved almost directly southward during the first half of December, and dropped below the horizon for most Northern Hemisphere observers shortly after mid month. As Northern Hemisphere observers caught their last glimpse of the comet, they generally estimated the magnitude as near 5, the coma diameter as about 20 arcmin, and the tail as over 1° long.

The comet faded slowly as it headed southward, because its increasing distance from Earth was nearly compensated by its decreasing distance from the sun. The magnitude was near 6 around the end of December and early January. The comet passed perihelion on January 22, at which time observers were typically giving the magnitude as 6.2-6.3. Although the comet should have began fading more rapidly, it surprized everyone when it was found to be experiencing an outburst on January 27. Estimates of the magnitude on that day, as well as on the 28th, placed it around 4.6-4.8. Interestingly, the comet appeared to have not been finished, as Michael Mattiazzo (Wallaroo,South Australia) found the comet near magnitude 3.0 on January 29.78. During the next few days, observers in the Southern Hemisphere saw the comet brighten to about magnitude 2.5, before it resumed fading.

Kronk’s website comet C/2000 WM1 (LINEAR)