Home=Current Comets: C/2023 H2
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Using the 1.5m reflector on Mt. Lemmon an asteroidal object was discovered on Apr. 23, 2023 near the border of the constellations Bootes/Canes Venatici, which showed cometary morphology in the course of follow-up observations. Comet C/2023 H2 (Lemmon) showed a 12" coma of total magnitude 20.0 with a central condensation, but no tail. The comet will pass perihelion at the solar distance of 0.89 AU on Oct. 29, 2023, expected to be of magnitude 13 around that date. During the following weeks it approaches Earth, passing it at a distance of only 0.193 AU on Nov. 11, predicted to reach magnitude 11, showing a coma diameter of about 4' (according to my empiric formula) (CBET 5264). It should be brighter than 16 mag between mid-September and late December 2023. During this period it moves through the constellations Ursa Major, Canes Venatici (perihelion), Bootes, Hercules (perigee), Aquila, Capricornus, Piscis Austrinus and Grus. From central European locations it can be observed both in the morning and evening skies until the first week of November, having greater altitudes in the morning sky until end of October. Around Nov. 25 it will disappear above the southern evening horizon. Earth will cross the comet's orbital plane on Oct. 31.
The comet could be easily spotted in binoculars at the beginning of November 2023 and became the third brightest comet of 2023! Based on 200 observations from 54 observers (until the start of February 2024) there was an above-average increase in activity pre-perihelion and a significantly below-average decrease in activity post-perihelion. brightness development can be represented quite well with the following parameters:
pre-perihelion : m0 = 10.6 mag / n = 5The maximum brightness of 6.4 mag was reached on the day of perigee. Thereby the apparent brightness showed a very similar development before and after the date of perigee. The comet was of magnitude 14.5 at the beginning of the apparition and of magnitude 12.5 at the beginning of January 2024.
Total Brightness and Coma DiameterThe same applies to the apparent coma diameter. It measured 1.5' in mid-September, reached a maximum of 17' at perigee and measured 1.5' again at the beginning of January 2024. The absolute coma diameter measured 125,000 km in mid-September, reached 200,000 km at the end of October 2023 (around the days of perihelion) and had shrunk to 125,000 km at the beginning of January 2024. The coma was rather diffuse. The degree of condensation increased only slightly from DC 2-3 to DC 3-4 during the days of perigee, and was DC 3 at the beginning of January 2024
Only a few CCD observers reported tail sightings between mid-October and the beginning of December, with the tail length reaching about 20' (300,000 km). Until Nov. 4 the tail was pointing almost due north, but then turned due east within a few days.
Andreas Kammerer