Analysis of Comet Apparitions

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12P/Pons-Brooks

2023/24

After more than 70 years comet 12P/Pons-Brooks (P=71.32a) will reach its 4th observed perihelion. On Apr. 21, 2024 it will pass the Sun at a distance of 0.78 AU. Since it will not get closer than 1.55 AU to Earth during this apparition and will move on the opposite side of the Sun as seen from Earth it is unlikely to become brighter than 4-5 mag. Around perihelion it should also reach its maximum coma diameter (about 10') and tail length (visual: about 2-3°), as indicated by my empiric formulae. The comet should be brighter than 16 mag between July 2023 and December 2024. During this period it moves through the constellations Draco, Hercules, Lyra, Cygnus, Lacerta, Andromeda, Pisces, Aries (perihelion), Taurus, Eridanus, Lepus, Canis Major, Puppis, Vela, Centaur, Lupus and Norma. As seen from mid-European locations it can be spotted quite low above the Northeastern morning horizon between December 2023 and February 2024. However, this comet is primarily visible in the evening sky at this apparition. While it is almost at the zenith at the end of twilight at the beginning of the apparition, it steadily loses altitude during the following months and will disappear above the WNW horizon in the first week of April 2024. The Earth will cross the comet's orbital plane on Dec. 8, 2023 and on June 6, 2024.

Since end of July 2023 the comet showed a very interesting development, displaying several outburst, the first of them accompanied with a very interesting coma morphology. The most conspicuous of these occurred on July 20/21 with an amplitude of 5 mag (brightening from 16.5 mag to 11.5 mag), which permanently increased its brightness by a factor of 100. During the following months the comet underwent two further major and several smaller temporary outbursts. The larger outbursts resulted in a significant increase of the total magnitude and led to a significant coma expansion. The smaller outbursts caused only a brightening of the central parts of the coma (near the nucleus) and an increase of the degree of condensation, but had only a small or no impact to the total magnitude. During the first outbursts the comet temporarily showed a compact coma of high surface brightness with a tailward appendage that showed a "shadow" behind the nucleus and thus had the shape of two "horns". Until end of January 2024 the listed outburst have been noticed: Sep. 3, 2023 (amplitude: ≈0.4 mag), Sep. 23/24 (0.9 mag), Oct. 4/5 (4.0 mag), Oct. 22/23 (≈0.4 mag), Oct. 30/31 (≈0.4 mag), Nov 14/15 (large), Nov. 30/Dec. 1, Dec. 13/14, Dec. 23, Jan. 17/18 (large) and Jan. 29. This behavior can be retraced quite well by applying moving weighted 3-days means.

Based on 690 observations by 76 observers the average brightness development can be represented quite well using the following parameters:

If the comet follows this development, it would reach a peak brightness of 5.5 mag ±1 mag around Apr. 21, 2024 (perihelion passage). It reached magnitude 7.5 in the first week of February 2024.

The development of coma diameter and degree of condensation also reflect the outburst behavior. Shortly after an outburst the highest DC values were reached (up to DC 8-9), which decreased rapidly during the following days. The coma diameter increased noticeably during the days following the outburst until the outer parts of the expanding coma reached the surface brightness of the sky background. Shortly afterwards the next outburst occurred with an initially small coma displaying a high surface brightness, which expanded over the following days (while the surface brightness decreased). So far the maximum coma diameter of 8' was observed as a result of the largest outburst (in July) in mid-September 2023, indicating an absolute diameter of 1.1 mio. km. In each of the following eruptions, both the apparent and absolute diameter did not reach these values. A tail has been observed since the end of August 2023. It reached a length of 15' (5 mio. km) on CCD images at the beginning of February 2024. During this period the tail changed its orientation from Southeast over East to NNW.

Andreas Kammerer

FGK observations