Analysis of Comet Apparitions

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156P/Russell-LINEAR

2020/21

Comet 156P/Russell-LINEAR (P=6.44a) will pass perihelion on Nov. 17, 2020 in the solar distance of 1.33 AU. It should peak at magnitude 15.0 two weeks earlier and should be brighter than 16 mag between September and December. During this period it moves from the southern part of Aquarius into the northern part of Pisces. For mid-European locations it should rise above the southern horizon late in the evening in mid-October.

The comet got distinctly brighter than expected during this apparition. Based on 235 observations from 44 observers the comet peaked at magnitude 9.7 around Nov. 15, 2020. Thus it got 5 mag brighter than expected! While the brightness increased extraordinarily fast prior to perihelion, it decreased significantly slower afterwards. In early April 2021 the comet had faded to 16 mag. The respective formulae are:

The apparent coma diameter increased quite steadily from 0.5' in mid-September to the maximum value of 5.5' around Nov. 20. Not until the opening of April had the diameter decreased to 0.5'. The absolute coma diameter increased from 10.000 km at the start of the apparition to its maximum of 150.000 km in mid-January. Thereafter it decreased more rapidly, reaching 35.000 km by early April.

Interestingly the coma got steadily more diffuse during the apparition. The degree of condensation decreased from DC 5 to DC 2-3. A tail, not exceeding 3' (150.000 km) could be observed between mid-November and mid-March. During this interval the tail rotated from ENE towards South.

Andreas Kammerer

FGK observations