Analysis of Comet Apparitions

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C/2017 T2 (PanSTARRS)

Images, taken by the PanSTARRS project on Oct. 2, 2017 showed a faint comet with a miniscule coma in the constellation Eridanus. Follow-up observertions of comet C/2017 T2 (PanSTARRS) showed a significantly condensed 12" coma of total magnitude 19.3 and a 20" tail in p.a. 290°. The comet will pass perihelion on May 6, 2020 in the distance of 1.62 AU. It is expected to peak at magnitude 8.0 during several weeks (CBET 4445). It should be brighter than 16 mag during the years 2019 and 2020, being brighter than 12.0 mag between October 2019 and October 2020. During the most interesting months it will be better positioned in the morning sky until November 2019 for mid-European observers. Thereafter it will be better observable in the evening sky until the opening of September 2020. During this time interval it will move through the constellations Taurus, Auriga, Perseus, Cassiopeia, Camelopardalis (maximum brightness), Ursa Major, Canes Venatici, Coma Berenices and Virgo.

Whereas the comet showed an average brightening pre-perihelion, post-perihelion it faded significantly more rapid, according to 1.237 observations from 85 observers. The appropriate formulae are:

Thus the comet peaked at 8.5 mag at perihelion. Until the opening of August 2020 the comet had faded to 10.5 mag. In combination with the decreasing altitude the comet became a difficult object for mid-European observers.

Until August 2019 the apparent coma diameter measured constantly 0.4'. Thereafter it increased steadily, reaching 6.5' at the end of April 2020. Until the end of May the diameter remained constant, thereafter decreasing towards 1.8' until mid-September. This results in an absolute coma diameter of 100.000 km until August 2019, and of about 225.000 km between September and November. Thereafter it showed a slight decrease to 200.000 km. Between the start of 2020 and the opening of April it swallowed from 260.000 km to the maximum of 500.000 km. Thereafter it shrunk, measuring 450.000 km at the end of June and 230.000 km in mid-September.

During the first period of the apparition the comet experienced a degree of condensation of DC 4. During the second period of the apparition the degree of condensation varied between DC 4 and DC 5 until the end of May 2020. Thereafter it decreased, reaching DC 2-3 at the end of July. During the whole apparition the coma showed a significantly condensed inner and a rather diffuse outer coma. In the central part a false nucleus of magnitude 12.0 could be discerned. A tail, curved significantly during much of the apparition, reaching a maximum length of 15' (2 Mio. km), was observed between August 2019 and May 2020. Until mid-November 2019 the tail pointed constantly towards Southwest, therafter rotating to Southeast until the end of January. Starting in April it rotated rapidly at first then gently towards Northwest.

Andreas Kammerer

FGK observations