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An asteroidal object, discovered by the "Zwicky Transient Facility" project on Mar. 2, 2022 in the constellation Aquila showed cometary morphology in the course of follow-up observations. Comet C/2022 E3 (ZTF) showed a highly condensed coma of diameter 15" and total magnitude 16.5 and a faint, 25" long tail in p.a. 310°. The comet will pass perihelion on January 12, 2023 in the solar distance of 1.11 AU and should then be of magnitude 7.5. On Feb. 2, 2023 it will pass Earth in the distance of 0.28 AU and could be as bright as magnitude 6, thereby showing a coma of about 15' (according to my empiric formula). It should be brighter than 16 mag between April 2022 and October 2023, brighter than 12 mag between October 2022 and April 2023. During the first interval it will move through the constellations Aquila, Sagitta, Vulpecula, Cygnus, Lyra, Hercules, Corona Borealis (perihelion), Bootes, Draco, Ursa Minor, Camelopardalis (perigee), Auriga, Taurus, Eridanus, Lepus, Canis Major, Puppis, Vela and Pictor, during the second interval it will move from Corona Borealis towards Eridanus. Thus, the comet will be a well-placed object during the most interesting weeks for mid-European locations, thereby changing from the morning into the evening sky.
This comet became the most interesting and brightest one in winter 2022/23. Under a very dark sky it could be glimpsed with unaided eyes as a pale small nebula. Based on 931 observations from 79 observers the brightness development can be well represented by the formula
m = 7.0 mag + 5×log D + 10.3×log rThus the comet showed an average development for an object which had passed Sun for several times. However it did not fully grew up to the predictions made at the start of 2023, being of magnitude 6.8 at perihelion (prediction at the opening of 2023: 6.0 mag) and peaking at magnitude 4.9 at perigee on Feb. 2, 2023 (prediction: 4.5 mag). It had faded to 12.0 mag at the end of April.
Total Brightness and Coma DiameterThe apparent coma diameter measured only 0.3' at the start of the apparition, increasing steadily and measuring 4' in mid-December 2022. This was followed by a rapid expansion to the maximum of 24' at the time of perigee. Immediately thereafter, it rapidly shrunk, measuring 5' at the beginning of March, 2.5' around March 20 and 1.5' around April 20. The absolute coma diameter remained fairly constant at about 75,000 km until late July 2022, thereafter increasing steadily. At the time of perihelion the coma reached the maximum size of 450,000 km. Thereafter it shrunk, measuring 300,000 km in mid-February and 175,000 km in mid-April 2023. The coma showed an interesting development of the degree of condensation: initially at DC 5-6 it decreased to DC 4-5 by the end of October, thereafter increasing again to DC 5-6 by mid-December 2022. In April 2023 it had decreased to DC 3.
A tail could be observed between June 2022 and March 2023, at first only by CCD observers, but starting in August also visually. At the end of the year it measured just 0.2°, but grew up to nearly 1.5° around the days of perigee. Thereafter a rapid shrinkage took place. In absolute dimensions the tail reached a first maximum of 1.75 mio. km in September 2022 and a similar maximum around Jan. 20, 2023. Initially the tail was oriented towards SSW, but turned to ESE by September and to ENE by early December. Then a more rapid change towards North took place until the end of the year. By Jan. 20 it had turned to NNW. Then, within just three weeks, it turned over West, South and East towards NE. Thus the tail increasingly deviated from the antisolar direction in summer/fall, reaching a maximum deviation angle of 60° in December 2022. During the days the Earth crossed the comet's orbital plane (Jan. 23) a conspicuous anti-tail could be recorded photographically.
Andreas Kammerer