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 has been observed since the beginning of 2024. From the beginning of January to the beginning of February the 31 observations by 14 observers show an increase in brightness from 16.0 mag to 13.5 mag. The resulting brightness parameters (with very good correlation) are
m0 = -3.0 mag / n = 16indicating a maximum brightness of 1.2 mag ±2.5 mag at the beginning of July 2024. However, the parameters have to be regarded as purely mathematical, since the comet was still faint at the start of the apparition (when systematic errors are larger), the time span is short and the number of observations is small. All of these facts result in an extreme uncertainty. Either the observations of the coming weeks will yield more plausible parameters or the comet will suffer a break in the brightness development. The international predictions, determined from earlier apparitions, are around 6-7 mag.
The coma diameter increased from 0.6' (60,000 km) to 1.0' (100,000 km) in the same period. The degree of condensation is around DC 5. A tail has not yet been observed.
Andreas Kammerer