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On March 9, 2021 the search program "Zwicky Transient Facility" (ZTF) discovered a 19.5 mag asteroidal object near the border of the constellations Cygnus/Vulpecula, moving on a near-parabolic orbit. Follow-up observations showed cometary morphology. Comet C/2021 E3 (ZTF) displayed a significantly condensed 8" coma of total magnitude 19.0m and a 7" tail pointing towards p.a. 335°. The comet will pass perihelion at the solar distance of 1.78 AU on June 11, 2022, expected to reach magnitude 12.0 (CBET 4960). It should be brighter than 16 mag between November 2021 and February 2023. During this period it moves from the constellation Aquila towards Capricornus and Microscopium, thereafter entering the far Southern Sky. From mid-European locations it will disappear above the evening horizon in December 2021 (at a predicted magnitude of only 15.5).
The comet got 2.5 mag brighter than initially predicted. At the time it appeared in the morning sky (at the start of March 2022) it was already of magnitude 12.0 and brightened further, reaching 10.0 mag in early May. Based on 68 observations from 14 observers the brightness development can be well described by the parameters
m0 = 5.6 mag / n = 6.3
yielding a maximum brightness of 9.3 mag at the opening of June 2022. Total Brightness and Coma DiameterThe coma diameter increased from 2' (160.000 km) at the start of the apparition to the maximum of a bit more than 5' (275.000 km) at end of May 2022. Until mid-July it had shrunk to 1.5' (125.000 km). Throughout the apparition the comet showed a constant degree of condensation of DC 4. Between the opening of May and end of July 2022 a tail was observed, reaching a length of 12' (1.5 Mio. km) in mid-June. Until end of May the tail pointed towards NW, then began to rotate, pointing towards SSE at the end of June.
Andreas Kammerer