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Analysis of Comet Apparitions


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C/2020 T2 (Palomar)


On images taken with the 1.2m-Schmidt-telescope at Palomar Observatory on Oct. 7, 2020 a comet was discovered near the borders of the constellations Leo/Leo Minor/Ursa Major. Follow-up observations of comet C/2020 T2 (Palomar) showed an 8" coma of total magnitude 18.5 and a 6" tail in p.a. 310°. The comet will pass perihelion at the solar distance of 2.05 AU on July 11, 2021 (CBET 4870). Assuming n=3 for a dynamically "new" comet it should peak at magnitude 14.0 in May 2021. It should be brighter than 16 mag between February and September 2021. During these months it will move through the constellations Canes Venatici, Bootes, Virgo and Libra. From mid-European locations the comet will disappear as an object of magnitude 15 below the southwestern evening horizon at the end of August.

In total 343 observations from 46 observers have been published which I could use for the analysis (with the number of observations decreasing after August due to deteriorating observing conditions). The number of observations is astonishingly great for a comet of just 10-11 mag. However, this comet was situated in the evening sky and had no rivalry with other comets for a long time. The observations clearly indicate a very different development pre- and post-perihelion. It quickly increased in brightness pre-perihelion, whereas post-perihelion the heliocentric magnitude faded considerably slower. The derived formulae are as follows:

pre-perihelion : m = -1.2 mag + 5×log D + 34×log r
post-perihelion: m = +5.7 mag + 5×log D + 11×log r

Thus the comet peaked at magnitude 10.2 around June 25, 2021.

Total Brightness and Coma Diameter

Until mid-March 2021 the apparent coma diameter increased slowly from 0.5' to 1.0'. This was followed by an interval of more rapid increase until end of May. The maximum coma diameter of 4.7' was reached at the start of June and hold until end of July. Thereafter it decreased slowly, measuring short of 3' on Oct. 10. Until mid-March 2021 the absolute coma diameter was constant at about 80.000 km, increasing to 375.000 km until mid-July. This value was constant during the following weeks. The coma was rather diffuse (DC 3) at the start of the apparition, increasing to DC 4 at the start of April. The degree of condensation was constant during the following weeks, except for the periods May 10 to 25 and July 25 to Aug. 15, when it increased to DC 5-6.

Tail sightings have been reported between end of January and end of July 2021. The tail reached a maximum length of 10' (1.5 Mill. km) around perihelion. During its appearance it rotated from WNW towards South and then ESE.

Andreas Kammerer

FGK observations


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