Analysis of past comet apparitions

C/2000 W1 (Utsunomiya-Jones)

On Nov. 18, 2000, Syogo Utsunomiya reported the visual discovery of a 8m bright comet in the constellation Vela with a 25x150 binocular. It showed a fast movement to the south-east and had an apparent coma diameter of 5'. However, confirmational observations by others were without success. In the morning of Nov. 25, the well-known amateur Albert F. Jones of New Zealand noticed a comet with a 4' diffuse coma while observing the variable star T Aps with his 8cm refractor. Further observations showed that the comet was quite close to Earth, having reached minimum distance of 0.28 AU on just that day. This comet passed its perihelion on Dec. 26 at a solar distance of 0.32 AU (IAUC 7526/27). It is noteworthy that Albert Jones, aged 80, is the oldest comet discoverer so far. He discovered another comet, also while observing a variable star, namely comet Jones (1946VI), which reached a max. brightness of 6m. Albert Jones is also the person with the longest comet discovery time span - 54 years! (The Astronomer, Dec. 2000, ICQ Oct. 2000)!

A first analysis of 50 international observations presents the following results: due to its low absolute brightness the comet did only reach 6m, not being observable then because of its proximity to the sun. The brightness evolution may be described by the following formulae:

pre-perihelion: m = 10.2m + 5×log D + 10×log r,

post-perihelion: m = 11.0m + 5×log D + 10×log r.

Due to the close proximity to Earth the coma diameter was largest at the time of discovery with 10' (200.000 km), but decreased rapidly in the following weeks and was only 2-3' (120.000 km) at the end of January. The evolution of the DC-value can not be described by now.

Total Brightness and Coma diameter

Observations on Feb. 12, 2001 with the 1.5m Catalina Reflector showed that this comet had undergone a rapid fading with the the 1.7' coma showing a R-band brightness of only 16.5m while observers reported visual magnitudes near 11.5m at the end of January. No condensation brighter than 21m could be detected (IAUC 7586). Observations by A.C. Gilmore with the 1m-Telescope of the Mount John Observatory on March 3 showed only a diffuse parabolic glow at the expected comet's position. The glow was brighter and 1' wide at the 'head' end; the 'tail' was more than 10' long (PA=80°) and 2' wide at the end. No condensation brighter than R=20m was found (IAUC 7594). Thus the number of disintegrated comets during recent years has further increased.

Andreas Kammerer