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Analysis of Comet Apparitions

19P/Borrelly

2021/22

Comet 19P/Borrelly (P=6.84a) will pass perihelion on Feb. 2, 2022 at the solar distance of 1.31 AU, predicted to reach magnitude 8. For mid-European latitudes it will appear around Dec. 10, 2021 - 10 mag bright - above the southern evening horizon, positioned in the constellation Sculptor. Until perihelion it will move northward into the area Pisces/Aries, thus should be well observable beginning near year's end. Therafter it will slowly fade, expected to reach magnitude 16 in May. Between February and May it will move through Aries, Perseus, Auriga and Lynx. The comet is highest in the evening sky in March, thereafter will slowly sink towards the northwestern horizon. Earth crosses the comet's orbital plane on Dec. 6, 2021.

Based on 426 observations from 56 observers the comet showed different brightness developments pre- and post-perihelion which can be well represented by the following formulae:

pre-perihelion: m = 5.2 mag + 5×log D + 28.5×log r
post-perihelion: m = 7.3 mag + 5×log D + 11.1×log r

Thus the comet brightened significantly more rapid pre-perihelion than it faded post-perihelion. At magnitude 17 at the start of the apparition the comet peaked at 9.0 mag at the end of January 2022. It was still of magnitude 11.5 in early May 2022.

Total Brightness and Coma Diameter

Between end of August 2021 and end of January 2022 the coma diameter increased from 0.5' (25.000 km) to the maximum of 6.5' (325.000 km). This value was hold for the next four weeks. Thereafter it decreased steadily, measuring still 2' (225.000 km) in early May. Interestingly the coma got more diffuse during the whole apparition, with the degree of condensation decreasing from DC 5-6 at the start of the apparition to DC 2-3 in early May 2022 and DC 2 in July. Only around perihelion did it temporarily increase to DC 5. A tail was reported between early January and end of March 2022, reaching 0.5° (2.5 Mio. km). It was oriented constantly towards ENE.

On images taken by Gerald Rhemann on Nov. 1 and 2, 2021 a narrow dust band can be detected in front and behind the comet, which could be followed for at least 1° in both directions. Whereas both parts showed an equal surface brightness on the mentioned dates the part in front of the comet was much fainter on Nov. 22 (CBET 5080).

Andreas Kammerer

FGK observations

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