Analysis of Comet Apparitions

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88P/Howell

2020/21

Comet 88P/Howell (P=5.48a) will pass perihelion on Sep. 26, 2020 at the solar distance of 1.36 AU, expected to peak at magnitude 9.0^m during those days. In February it should become brighter than 16 mag. During spring and summer 2020 it will loop in Virgo, thereafter will move – along the ecliptic – through the constellations Libra, Scorpius (perihelion), Ophiuchus, Sagittarius towards Capricorn. Moving through Aquarius and Pisces it should get fainter than 16 mag around February/March 2021. For mid-European locations the comet will be lost in the dusk at the end of June – expected to be of magnitude 11-12.

For the analysis of the development of this comet 279 observations from 35 observers could be used. These clearly show a very different development of the brightness pre- and post-perihelion, as the following formulae demonstrate:

Thus the comet peaked at magnitude 9.0 around Sep. 25, 2020.

The apparent coma diameter increased steadily from the start of the apparition (0.3') to the maximum of 6' which was hold between mid-September and the opening of October 2020. Thereafter the diameter shrunk in a similar manner, reaching 1.5' in mid-January. Between the start of the apparition and mid-September the absolute coma diameter increased steadily too, from 25.000 km to 350.000, then much slower until it reached the maximum value of 375.000 km at the opening of October. Thereafter it shrunk slowly, reaching 275.000 km by mid-December. This was followed by a period of faster shrinkage with the coma reaching 100.000 km in mid-January. Most of the apparition the coma was rather diffuse with a degree of condensation of DC 3. Between mid-September and mid-October the coma was slightly more condensed (DC 4). Only very few tail sightings have been reported, with a maximum length of no more than 2' (600.000 km).

Andreas Kammerer

FGK observations