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 shows a very smooth development slightly above average for a "new" one. However, because of the larger solar distances the brightness develops rather slowly. Based on 701 estimates from 62 observers (until the end of October 2023) the brightness development can be well described by the formula

m = 4.8 mag + 5×log D + 8.6×log r

Accordingly the comet showed a first peak of 9.9 mag during the second half of January 2023. Because Earth receded from the comet until perihelion the brightness faded a bit during the following weeks towards 10.2 mag. Thereafter the comet brightened again, reaching maximum brightness of 9.8 mag in the first half of September 2023.

Total Brightness and Coma Diameter

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'. 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. 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). 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.

Andreas Kammerer

FGK observations