Home=Current Comets: C/2023 A3
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The "Asteroid Terrestrial-Impact Last Alert System" (ATLAS) team discovered an 18th magnitude asteroidal object on Feb. 22, 2023 near the border of the constellations Serpens/Libra/Virgo. Subsequently, Minor Planet Center staff identified three positions of a Jan. 9, 2023 object assumed lost, which had been transmitted from China's Purple Mountain Observatory, with the asteroidal object. Since comets discovered by this observatory are designated Tsuchinshan by Chinese astronomers, this comet was given the designation C/2023 A3 (Tsuchinshan-ATLAS). Additional observations of the comet in the last days of February showed a strongly condensed 6" coma of total magnitude 18.0, but no tail. The comet will come quite close to both the Sun and Earth in the fall of 2024. It was at the large solar distance of 7.3 AU at the end of February 2023. Thus, it is a very interesting comet, but its activity level is currently very uncertain. In the following a new comet is assumed, whichs brightness increases with n=3. The comet will pass perihelion on Sep. 28, 2024 at the distance of 0.39 AU and could then reach 3rd magnitude (CBET 5228). Thereafter it will pass Earth on Oct. 13 at a distance of 0.47 AU, but will be near the Sun-Earth line und thus close to the Sun on the sky. Between November 2023 and September 2025 the comet should be brighter than 16 mag. During this period it will move through the constellations Libra, Virgo, Leo, Sextant, Leo/Crater (perihelion), Virgo (perigee), Serpens Caput, Ophiuchus, Serpens Cauda, Aquila, Delphinus, Vulpecula, Lyra and Hercules. For central European locations the first observing window will last from early December 2023 (15-16 mag, morning sky) to mid-June 2024 (11 mag, evening sky). The second, very unfavorable observation window lasts from about Sep. 25 to Oct. 5, 2024 (3-4 mag), but during this time the comet can only be seen extremely low above the eastern morning horizon during twilight. The third observation window is the most interesting. The comet will emerge above the western evening horizon on Oct. 12 (3-4 mag), reaching altitudes near 40° by early November, but fading to 6-7 mag during these two weeks. According to my empirical formulae, it should show a coma diameter of 20' during the days of greatest approach to Earth and a tail up to 5° long, which probably will be rather faint, thus difficult to observe visually. In the mid-January (11-12 mag) the comet disappears again above the western evening horizon. Exactly at this time it appears in the morning sky and finally reaches maximum elevations of 70° in June (14-15 mag). During the next weeks it will change to the night and finally to the evening sky, where it should become fainter than 16 mag. Overall an interesting, but probably not a spectacular object.
During the first ten months the comet developed favorably. Based on 108 observations from 21 observers the brightness development can be represented very well with the parameters
m0 = 3.8 mag / n = 4.5If the comet maintains these development until perihelion it would peak at -1.0 mag ±1 mag at Oct. 5! However, it must be emphasized that this is a purely mathematical result that does not take into account systematic errors, which are particularly common for faint comets. A reliable statement should be possible in about three months. So far, the brightness has increased from 17.0 mag in April 2023 to 13.5 mag at the end of January 2024.
Total Brightness and Coma DiameterThe coma diameter measured 0.3' (75,000 km) during many months, but had increased to 0.6' (110,000 km) by January 2024. So far the coma is strongly condensed (DC 7). A tail appandage, oriented towards NW, has been recorded since December 2023 by CCD observers.
Andreas Kammerer