Analysis of Comet Apparitions

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C/2016 M1 (PanSTARRS)

On June 22, 2016 the PanSTARRS project discovered a 19 mag comet in the constellation Draco. Additional observations of comet C/2016 M1 (PanSTARRS) showed a 10" coma of total magnitude 18.5 and a 12" tail in p.a. 180°. The comet will pass perihelion in August 2018, expected to peak at 9 mag (IAUC 4286 / MPEC 2016-N14). It will be brighter than 16.0 mag between April 2017 and the end of 2019. It will switch from the morning to the evening sky in December 2017 and should be observable for mid-European observers until the opening of June 2018 (then at 9 mag). During this period it will move through the constellations Draco, Hercules, Ophiuchus, Serpens, Aquila and Sagittarius.

Based on 311 observations from 35 observers the comet showed a continuous brightness development slightly above average pre-perihelion. Post-perihelion the development has to be split in two intervals: during the first 130 days after perihelion (until about Dec. 20, 2018) the comet showed a constant heliocentric magnitude (i.e. a constant activity). Thereafter it decreased in a similar way as the heliocentric magnitude increased pre-perihelion, however at greater absolute magnitude. The brightness peaked at 8.5 mag around July 1, 2018. The appropriate formulae are:

t < 0d: m = 3.1 mag + 5×log D + 13.8×log r
0 < t < +130d: m = 7.9 mag + 5×log D
t > +130d: m = 2.2 mag + 5×log D + 13.3×log r

The apparent coma diameter remained constant at 0.6' until April 2018, thereafter increasing rapidly to the maximum value of 6', which was hold between mid-May and the start of August. Until October 2018 it decreased uniformly to 2.5' (primarily because of the then increasing distance Earth comet), but surprisingly started to increase again thereafter (despite an increase in the distance Earth comet), reaching 3.5' in mid-January 2019. At the end of April it measured 1.5', and 0.5' at the end of July.

Total Brightness and Coma Diameter

During the first months the absolute coma diameter was constant at 130.000 km, thereafter increasing rapidly, reaching a first maximum of 425.000 km at the end of July 2018. Until the start of October it decreased to 270.000 km, but astonishingly showed another increase thereafter, reaching 525.000 km in mid-January 2019. At the end of May it measured 225.000 km, and 100.000 km at the end of July. Throughout the apparition the coma was significantly condensed. In 2017 the observers reported a degree of condensation of DC 3. At the beginning of 2018 the DC began to increase, reaching DC 5-6 at the opening of September 2018. Thereafter it decreased, reaching DC 3-4 in October 2018 and DC 2 at the end of May 2019. Between mid-June and mid-August 2018 a tail could be observed visually, reaching a maximum length of 7' (2.5 Mio. km), pointing constantly northward.

Andreas Kammerer

FGK observations