On Aug. 23, 2004 the american amateur Roy A. Tucker discovered a 14 mag comet in the constellation Cetus on a CCD-exposure taken with his 35cm-telescope. Comet C/2004 Q1 (Tucker) showed a 50" coma and a 70" tail towards p.a. 230°. On Aug. 25. he measured a coma diameter of 30" and a 40" tail towards p.a. 255°. The comet will pass perihelion in December, moving from Andromeda into Cassiopeia, expected to reach 13 mag based on the very first estimates (IAUC 8393). However, September estimates seemed to point to a maximum brightness of about 11.5 mag.
The comet showed an unusual high activity factor n pre-perihelion, based on 45 observations by 8 members of the German Comet Section and 230 international observations (until mid-May 2005). In contrast, the post-perihelion fading was much slower. The brightness evolution can be described pretty good by the following formulae:
pre-perihelion: m = -0.7m + 5×log D + 34×log r
post-perihelion: m = 8.0m + 5×log D + 6.5×log r
Due to the high activity factor the comet showed a significant brightness increase, although the variation in solar distance was quite small. The maximum brightness was reached in mid-November 2004 at 10.5 mag.
Total Brightness and Coma diameter
The apparent coma diameter increased continuously from 1.3' at the beginning of the apparition to 3.5' in mid-November 2004. Thereafter it decreased in a similar manner during the following weeks, with the rate decelerating in February 2005, reaching 1.0' in mid-May. The absolute coma diameter increased from 100.000 km during the first days to 220.000 km at the end of December 2004. Since then it is decreasing at a constant rate, reaching 125.000 km in mid-May 2005. The degree of condensation remained constant at DC 3-4 until the end of the year 2004. Since then it slowly decreased to DC 3 (in mid-May). Visual tail observations were rare, only few observers reported one, up to 0.15° tall, between the beginning of October 2004 and mid-January 2005.
Andreas Kammerer
