Analysis of Comet Apparitions

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On images taken on Jan. 9, 2022 the PANSTARRS team discovered a comet of magnitude 20 near the border of the constellations Corvus/Crater. Follow-up observations of comet C/2022 A2 (PANSTARRS) showed a strongly condensed coma of only 2", without a tail. It will pass perihelion at the solar distance of 1.74 AU on Feb. 18, 2023, expected to peak at about 14 mag (CBET 5093). It should be brighter than 16 mag between November 2022 and August 2023. During this period the comet will move through the constellations Coma Berenices, Canes Venatici, Bootes, Draco, Cygnus (perihelion), Lacerta and Andromeda. Observers at mid-European locations can follow the comet in the morning sky, and in February/March 2023 in the evening sky too.

The comet showed a surprisingly positive development and became 5 magnitudes brighter than originally predicted! A total of 330 observations from 52 observers (until the end of October 2023) show a very steady development and an activity above average, with the comet peaking at magnitude 9.1 during the last days of January 2023. The brightness development can be well represented with the formula

m = 5.0 mag + 5×log D + 12.5×log r

The comet faded to 13.5 mag by the end of October. However, inspecting the brightness estimates closer shows a period of enhanced activity in August and September 2023.

Total Brightness and Coma Diameter

The apparent coma diameter increased from just over 3' in mid-November 2022 to the maximum value of 6' by mid-December 2022, remaining constant until early February 2023. It then shrunk, measuring only 2' by the end of June. The increase in activity in August/September 2023 also detectable in the development of the coma diameter: whereas it measured short of 2' at the beginning of August the observers estimated 3' in mid-September. By mid-October it had shrunk to 1.5'. The absolute coma diameter was initially 350,000 km and increased to the maximum value of 450,000 km by early December 2022. Thereafter the coma decreased steadily and measured only 300,000 km by the end of April 2023 (remaining constant until at least end of June). The short-term increase in activity in August/September 2023 led to a temporary expansion of the coma from 175,000 km at the beginning of August to 275,000 km in mid-September. Thereafter it shrunk, measuring 175,000 km in mid-October.

The degree of condensation increased from DC 3 at the beginning of the apparition to DC 4 during the Christmas days 2022. Thereafter the degree of condensation slowly decreased and was back to DC 3 at the end of June 2023. The short-lived activity increase in late summer 2023 did not result in an increase of the degree of condensation. Instead it steadily decreased, reaching DC 2 in late October. A northwest pointing tail could be detected between mid-December 2022 and mid-February 2023, reaching a maximum length of 10' (1.5 mio. km). As a result of the increase in activity in late summer 2023 the tail length shortly grew up to 12'. Because the associated absolute length would be more than 10 mio. km, the assumption of a noticeably curved tail is plausible.

Andreas Kammerer

FGK observations