Comet 22P/Kopff (P=6.40a) will pass perihelion at the end of October 2015, expected to peak at magnitude 9.5. Alas, for mid-European observers it will then be less than 10° above the evening horizon at the end of twilight.
During this apparition the comet showed a rapid brightening similar to the apparition of 2009, but remainded more than one magnitude fainter than 6 years ago. According to 29 visual and CCD observations by 4 members of the German Comet Section and 81 additional international observations the brightness evolution can be simulated – however with a greater uncertainty - by the formula m = 5.0 mag + 5×log D + 22×log r (formula in 2009: m = 4.4 mag + 5×log D + 22×log r). The comet reached a maximum brightness of 10.8 mag in mid-October 2015.
Total Brightness and Coma Diameter
The large scatter of the estimates could have been caused by the rather small altitudes of the comet for European and North American observers and by the very diffuse coma of the comet.The coma diameter decreased from short of 1' (65.000 km) at the start of the apparition to a maximum of 3.5' (325.000 km) at the opening of October. Thereafter it seems that the coma shrinks. The observers reported the degree of condensation between DC 2 and DC 2-3 throughout this apparition.
Andreas Kammerer
