Analysis of Comet Apparitions

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C/2020 V2 (ZTF)

On images taken by the Zwicky Transient Facility (ZTF) Project on Nov. 2, 2020 a comet of magnitude 19 was discovered in the constellation Coma Berenice. When it was realized, that the object moves along a near-parabolic orbit, detailed observations were undertaken, which showed a cometary morphology. Comet C/2020 V2 (ZTF) showed a diffuse 8" coma of total magnitude 18.5, but no tail. The comet will pass perihelion on May 8, 2023 in the solar distance of 2.23 AU (CBET 4887). In January 2023 it should peak at magnitude 11.5, moving through Cassiopeia. It should be brighter than 16 mag between start of 2022 and fall 2024. During this interval it moves through the constellations Canes Venatici, Ursa Major, Draco, Camelopardalis, Cepheus, Cassiopeia, Andromeda, Triangulum, Aries, Cetus, Sculptor, Grus towards Tucana. At mid-European locations it will be well-placed around perihelion. It will disappear from the evening sky (constellation Triangulum) at the start of April 2023, but will be visible again (in the morning sky) between mid-July and mid-September 2023 (Cetus).

The comet showed a very smooth and – caused by the larger solar distances - rather slow development. Based on 739 observations from 62 observers (until the start of May 2024) the brightness development was a bit different pre- and post-perihelion and can be well described by the formulae

pre-perihelion: m = 4.6 mag + 5×log D + 8.9×log r
post-perihelion: m = 4.2 mag + 5×log D + 10.2×log r

Accordingly the comet showed two maxima of magnitude 9.8 – one around Jan. 20, 2023 and the other at the opening of September 2023. Because Earth receded from the comet between February and the perihelion passage the brightness faded a bit during this period to 10.2 mag. Thereafter the comet brightened again, on its way to the second maximum.

Total Brightness and Coma Diameter (standard time scale)

Total Brightness and Coma Diameter (compressed time scale)

The apparent coma diameter measured only 0.4' at the start of the apparition, then increased steadily over the following months, reaching 1.1' in April and 1.5' in September 2022. After a five-week period of a more rapid increase it reached its maximum of 3.8' by mid-December. This value remained constant until mid-February 2023, thereafter decreased to 2.8' by early April. In summer the coma measured constantly 3.5', but decreased to 2.0' in fall and to 1.2' at the end of January 2024. The absolute coma diameter increased very steadily from 90,000 km at the start of the apparition to 225,000 km in April and 250,000 km in September 2022. Then a rapid expansion to 375,000 km by mid-December followed. In summer 2023 the maximum value of 425,000 km was achieved. Thereafter the coma shrunk, measuring 250.000 km during fall/winter 2023/24. The degree of condensation fluctuated between DC 3-4 and DC 4-5 (in Jan/Feb 2023).

A tail can be detected since March 2022, with a length of up to 9' (2.5 mio. km) in Jan/Feb 2023. In summer 2023 the tail showed a length of constantly 15' (6 mio. km), which shortened to 8' (4.5 mio. km) in winter 2023/24. The tail orientation changed from SSE in March to East in August and again to SSE in mid-December 2022, then rapidly changed over East to NNE within two weeks. In summer 2023 the tail pointed constantly towards North and in winter 2023/24 towards NE.

Andreas Kammerer

FGK observations