Home=Current Comets: 13P (2024)
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On Aug. 24, 2023, Alan Hale rediscovered comet 13P/Olbers (P=69.25a) remotely with the 1.0m Schmidt-Cassegrain telescope at Las Cumbres Observatory. The stellar comet was located in the constellation Eridanus and had a magnitude of about 21.5 mag. The comet was observed during its last perihelion passage in 1956. The next perihelion passage at the solar distance of 1.18 AU will take place on June 30, 2024 with an expected maximum brightness of 7.5 mag (CBET 5289). At this time my empirical formulae predict a maximum coma diameter of 5-6' and a maximum visual tail length of just under 0.5°. It should be brighter than 16m between December 2023 and August 2025. During this period it will move through the constellations Eridanus, Cetus, Taurus, Auriga, Lynx (perihelion), Leo Minor, Ursa Major, Coma Berenice, Bootes, Virgo, Libra, Ophiuchus and Sagittarius. Observing from Central European locations it will be an object visible during the whole night in the first few weeks, but will change to the evening sky in January 2024. In February 2024 it will reach its maximum altitude of 35° before starting to sink towards the horizon. In the most interesting weeks (May to September 2024) it will unfortunately experience altitudes of less than 20° (in May even less than 10°). At the end of October 2024 it will disappear above the western evening horizon. From February to mid-June 2025 it will reappear in the morning sky, but the altitudes will be less than 15°. On June 17, 2024 and on Dec. 17, 2024 the Earth will cross the comet's orbital plane.
The comet was the primary object for comet observers in the summer months of 2024, being rather well visible in binoculars. However, the generally low altitudes were a hindrance. Nevertheless, at the beginning of February 2025 665 observations from 69 observers can be used for the analysis. These show a significant difference in the brightness development pre- and post-perihelion. Post-perihelion, the decrease in activity happened significantly slower than the increase in activity pre-perihelion. The formulae are as follows:
pre-perihlion: m = 3.8 mag + 5×log D + 20.0×log r post-perihlion: m = 4.5 mag + 5×log D + 10.8×log rOnly of magnitude 14.0 at the start of the apparition the comet brightened very steadily to the maximum of 6.5 mag at the beginning of July 2024. By the start of November the comet had faded to only 10.5 mag.
Total Brightness and Coma DiameterThe coma diameter increased from 0.8' (75,000 km) at the start of the apparition to 9' (750,000 km) by the opening of August 2024, thereafter shrinking, measuring 3' (400,000 km) at the start of November. The coma was only slightly condensed at the beginning and end of the apparition (DC 3), but in the weeks around perihelion it was significantly condensed (DC 6). A constantly ENE-directed tail was observed between mid-May and the end of September. This reached a maximum length of 40' (7 mio. km) at the beginning of August.
Andreas Kammerer