If comet 67P/Churyumov-Gerasimenko (P=6.45a) should evolve according to the ICQ-prediction, it should be observable with larger instruments as an object of about 13 mag during winter 2008/09. Moving from Capricornus into Aries it should be a comfortably placed evening object.
Actually this comet became much brighter than expected, reaching a maximum of 10.1 mag at the end of February 2009! According to 4 observations by 3 members of the German Comet Section and 35 international observations the brightness evolution can be well described by the formula
m = 6.7 mag + 5×log D + 24×log rThe apparent coma diameter was only 0.3' at first, increasing to 1.0' at the turn of the year and to 4' at the beginning of March 2009, remaining constant thereafter. The absolute coma diameter measured only 20.000 km at the beginning of the apparition. Starting at the turn of the year it increased, peaking at 325.000 km around Mar. 20, 2009. Thereafter it shrunk, measuring 200.000 km at the end of May. The coma was medium condensed until end of March (DC 3-4), but got more and more diffuse thereafter. At the end of May the degree of condensation was estimated as only DC 1-2.
Total Brightness and Coma Diameter
Andreas Kammerer
