The current apparition of comet 46P/Wirtanen starts in mid-November 2007 for mid-European observers. Situated in the constellation Piscis Austrinus it appears above the southern evening horizon. Thereafter it moves toward Aquarius, thereby gaining altitude and becoming brighter, reaching about 10 mag at the start of December. However, this comet normally shows a rather diffuse coma.
Despite the rather comfortable circumstances (evening sky) the number of observations published or received is surprisingly small, perhaps due to the large, rather diffuse coma it displayed. Only 38 observations by 7 members of the German Comet Section and additional 190 international observations could be used for the analysis. These show different brightness evolutions pre- and post-perihelion, according to the formulae
pre-perihelion: m = 8.3m + 5×log D + 22.5×log r post-perihelion: m = 8.6m + 5×log D + 14.5×log rwhat means that the comet reached a maximum brightness of 8.6 mag around Feb. 5, 2008.
Total Brightness and Coma Diameter
The evolution of the coma diameter was very similar pre- and post-perihelion. Both at the start and end of the apparition it measured 1.5' (90.000 km), reaching 7.5' (300.000 km) at perihelion. The degree of condensation was low. As of the coma diameter, it evolved in a similar manner, pre- and post-perihelion. It was at DC 2-3 at the beginning and end of the appartion, reaching DC 4 around perihelion. No tail was seen visually.
Andreas Kammerer
FGK observations