Analysis of Comet Apparitions

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On Oct. 22, 2023, comet 2P/Encke (P=3.30a) will pass its perihelion (at the solar distance of only 0.34 AU) for another time, expected to reach a maximum brightness of 7.0 mag. It should become brighter than 16 mag during July. From mid-European locations the comet can be observed above the Eastern morning horizon until mid-October, reaching a maximum altitude of 45° in early September. Between early August and mid-October the comet moves through the constellations Aries, Auriga, Gemini, Cancer, Leo into the western part of Virgo.

During this perihelion passage the comet was rather difficult to observe and only pre-perihelion, which is why only 76 observations from 37 observers can be used for the analysis. These show a brightness development that can be represented moderately well with the formula

m = 11.3 mag + 5×log D + 10.0×log r

It should be noted that the comet experienced the same parameters post-perihelion during its previous perihelion passage (in 2020)! The comet thus reached a maximum brightness of 7.0 mag at perihelion. From Earth the maximum observed brightness was 8.0 mag (on Oct. 12).

Total Brightness and Coma Diameter

The coma diameter increased from 1.5' (100,000 km) at the beginning of the apparition to a maximum just short of 4.5' (175,000 km) around Sep. 25. On Oct. 12 the observers estimated a coma diameter of only 1.5' (70,000 km), most probably due to the increasing solar wind. While approaching the Sun the coma condensed considerably with the degree of condensation increasing from DC 2 to DC 8. No tail observations have been published.

Andreas Kammerer

FGK observations