Comet 67P/Churyumov-Gerasimenko (P=6.44a), currently under the surveillance of the Rosetta probe, will reach perihelion in mid-August 2015. For mid-European observers it will appear above the northeastern morning horizon at the start of August 2015. During the weeks following it will quickly gain altitude. Assuming the ICQ brightness parameters which represent the published observations rather well, it should peak at 10-11 mag at the end of August. Between August and year's end of 2015 it will move from Taurus into Virgo.
The comet showed a significantly asymmetric brightness evolution, as indicated by 24 observations of 4 members of the German Comet Section and 58 international observations. As it was the case during the previous perihelion passages, the brightness evolution can only be described by time-dependent formulae. In addition, the heliocentric magnitude continued to increase until 25 days after perihelion, thereafter decreased at a slower rate. It can be described by the following formulae:
t < +25d: m = 11.0 mag + 5×log D + 0.032×(t-T) t > +25d: m = 9.8 mag + 5×log D + 0.016×(t-T)The maximum brightness of 11.2 mag was reached around Sep.10.
Total Brightness and Coma Diameter
The coma diameter increased from 0.35' (35.000 km) in early July to a maximum value of 1.5' (120.000 km) in mid-September. Thereafter it decreased, reaching 0.5' (30.000 km) at the end of January 2016. The coma was only moderately condensed (DC 2-3) in July, but got more condensed until mid-September (DC 4-5), only to get more diffuse again thereafter. Using CCD images a tail could be detected pointing westward, reaching a maximum length of 15' (2 mio. km) in October.Andreas Kammerer
