Home=Current Comets: C/2021 S3
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On Sep. 24, 2021 the PANSTARRS team discovered a 19.5 mag comet in the constellation Lepus, which showed a 2" coma. Additional observations of comet C/2021 S3 (PANSTARRS) showed that this comet was still at a distance of 9 AU from the Sun, displaying a compact, 6" coma. It will pass perihelion on Feb. 18, 2024 at the solar distance of 1.33 AU, predicted to become as bright as 9 mag (CBET 5051 / MPECs). It should be brighter than 16 mag between February 2023 and January 2025. During this period it will move through the constellations Columba, Lepus, Canis Major, Puppis, Circinus, Antlia, Centaurus, Lupus, Scorpius, Ophiuchus/Serpens (perihelion), Aquila, Sagitta, Vulpecula towards the border of Cygnus/Draco, where it will display an opposition loop. It should be brighter than 12 mag between November 2023 and July 2024, when it will move from Centaurus to Cygnus/Draco. At mid-European locations it will appear above the southern morning horizon in February 2024, will then climb up and culminate at altitudes of 75° in June/July 2024. Thereafter it changes to the whole-night and evening sky, at which it will sink slowly down.
The comet was not an easy object, as is also indicated by the rather small number of observations regarding its peak brightness. For the analysis 329 observations from 54 observers can be taken into account. These indicate different brightness developments pre- and post-perihelion, with the activity surprisingly increasing significantly slower pre-perihelion than it decreased post-perihelion. The following formulae represent the brightness development well:
pre-perihelion: m = 8.4 mag + 5×log D + 5.0×log r post-perihelion: m = 8.4 mag + 5×log D + 7.2×log rThus the comet peaked at 9.7 mag around Feb.20, 2024. The comet was of magnitude 15.5 at the start of the apparition, brightening slowly at first, but ever more rapidly during the following months. After the comet had peaked it faded to 11.0 until the start of May 2024 and to 16.0 mag at the end of 2024.
Total Brightness and Coma Diameter (standard time scale)
Total Brightness and Coma Diameter (compressed time scale)
The apparent coma diameter increased from 0.3' to 1.3' between the end of 2022 and the end of 2023, reaching a maximum of 2.7' in February 2024. Thereafter it shrunk, measuring 1.5' at the start of August and 0.7' at the end of October. The absolute coma diameter measured about 100,000 km until the end of 2023, peaking at 190,000 km at the start of March 2024. Thereafter it shrunk, measuring still 150,000 km at the opening of August and 100,000 km at the end of October. The degree of condensation was constant at DC 4-5 until Apr. 10, 2024, thereafter decreased significantly to DC 3 until the start of May and to DC 2 at the end of October. A tail was observed between October 2023 and April 2024, which reached a maximum length of 0.3° (4 mio. km) in summer 2024. It pointed towards WSW to West.Andreas Kammerer