Comet 2P/Encke will pass perihelion in mid-April 2007 and should become observable with larger instruments at the end of January. It will disappear above the western horizon during the first week of April. However, throughout the apparition it will be very low above the western horizon at the end of twilight (for example 20° at the start of March). During this time it will move from Pisces to Aries.
Werner Hasubick was the only observer of the German Comet Section who succeeded in visually observing comet 2P/Encke during this apparition. But internationally it was not observed widely, too, so that the following analysis can only give a crude overview. Nevertheless the few observation reports indicate a different brightness evolution before and after perihelion, which can be described by the formulae
pre-perihelion: m = 10.3m + 5×log D + 7.8×log r
post-perihelion: m = 11.8m + 5×log D + 12.5×log r
The apparent coma diameter increased until perihelion from 2' to 3.5'. Therefore the absolute coma diameter measured 200.000 km until mid-March, thereafter decreasing until perihelion to 160.000 km and until mid-May to 80.000 km. In parallel the coma became more condensed until perihelion, with the degree of condensation increasing from DC 2-3 to DC 6. In mid-May the coma it had become quite diffuse again (DC 2).
Total Brightness and Coma diameter
On Apr. 8 Michael Jäger found two thin, faint arclets, positioned approximately at right angles in respect to the main tail; on his images. Further investigation on Apr. 12 confirmed the north pointing arclet. At first the nature of these arclets was unclear, speculations included very unusual jets or a dust band along the orbit of the comet, already found at other periodic comets. This arclets however were irritating, because they were not straight but curved. Simulations by Masayuki Suzuki then confirmed the dust band interpretation: during those days the projection of the orbit on the sky globe was actually curved.
Andreas Kammerer
