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On Dec. 26, 2021 an asteroidal object of magnitude 18.5 was discovered by the ATLAS project near the borders of the constellations Cassiopeia/Perseus/Andromeda. Follow-up observations identfied the object as a comet. Comet C/2021 Y1 (ATLAS) showed a strongly condensed coma of diameter 10" and total magnitude 17.5, but without a tail. It will pass perihelion in the solar distance of 2.03 AU on May 1, 2023, expected to peak at magnitude 12.5-13.0 between end of 2022 and mid-2023 (CBET 5089). The comet should be brighter than 16 mag between August 2022 and February 2024. During this period it will move through the constellations Perseus, Auriga, Taurus, Eridanus (perihelion), Columba, Puppis, Vela, Centaurus, Lupus and Norma. During the first months the comet will be a morning object, switching to the evening sky at the turn of 2022/23, disappearing for mid-European observers at the opening of March 2023 above the southwestern horizon (at magnitude about 12.5-13.0).
Based on 64 observations from 14 observers the comet shows a development above average which can be represented by the parameters
m0 = 6.7 mag / n = 6
Thus the comet peaked at 13.3 mag between mid-April and mid-May 2023. The diameter of the significantly condensed (DC 5) coma increased from 0.4' (60,000 km) in August 2022 to 0.8' (75,000 km) in October 2022 and to 1.2' (100,000 km) in March 2023. Beginning in November 2022 a tail of up to 3' (800,000 km) length, pointing towards North to Northeast, was detected.
Total Brightness and Coma Diameter
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On images taken with the 1.5m-reflector at Mount Lemmon on Nov. 26, 2022 Gregory Leonard discovered a comet in the constellation Leo Minor. Comet C/2022 W3 (Leonard) showed a medium-condensded 6" coma of total magnitude 19.5 and a broad 10" tail in p.a. 240-260°. The comet will pass perihelion in the solar distance of 1.40 AU on June 22, 2023, expected to reach magnitude 15.0. Until mid-August it will approach Earth, passing it in the distance of 0.76 AU and could then peak at magnitude 14.0 (CBET 5204). It should be brighter than 16.0 mag between May and September 2023. During this period it will move through the constellations Cassiopeia (perihelion), Cepheus, Cygnus (perigee), Vulpecula, Sagitta, Aquila, Scutum and Sagittarius. From mid-European locations it will be visible in the morning sky during the beginning, but will change to the evening sky by mid-August. During the first weeks it will be visible the whole night through. Earth will cross the orbital plane on Aug. 5.
The analysis can be based on 30 observations from 11 observers, which show a very large scatter. Thus the brightness development can be brepresented only with a rather large uncertainty by the parameters
m0 = 13.5 mag / n = 2
The comet peaked around magnitude 14.0 in July 2023. The estimates give a maximum diameter of the coma of 1.0' (60,000 km). CCD observers could detect a short tail.
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In publicly available SWAN images (which image the sky in UV) between January 6 and 13, 2023, Ukrainian Vladimir Bezugly discovered a moving object that he thought was a comet of about magnitude 12. After the publication in the Comet's Mailing List an intense search in the images of various probes followed. Finally the comet could be confirmed in STEREO images taken on Feb. 1. Already on January 30, K. Yoshimoto was able to detect the comet with an 8cm refractor and CCD as a 12.7 mag bright object with a 1.3' coma at the southern boundary of the constellation Aquila. Additional CCD observations in mid-February showed an object of about magnitude 13.0 with a very condensed coma of diameter about 1.5', but no tail. Comet C/2023 A2 (SWAN) passed perihelion at the solar distance of 0.95 AU on Jan. 20, 2023 (CBET 5226). Since it was on the opposite side of the Sun from Earth, its elongations were small and thus the comet was difficult to observe. Although the elongations will increase in the coming weeks, it will move to the southern sky and remain unobservable from central European latitudes. Around mid-May it should get fainter than 16 mag.
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Comet C/2023 B2 (ATLAS), discovered on Jan. 21, 2023, was predicted to peak at about magnitude 16.5. However it seems that this comet experienced a minor outburst lasting about 5 weeks, starting in mid-April 2023 – four weeks after perihelion. It reached magnitude 14.5, showing a coma diameter of about 1'.
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On April 18, 2023 R. Matson discovered a possible cometary object near the border of the constellations Eridanus/Cetus in SWAN data, moving rapidly southward. On the same day M. Mattiazzo succeeded in taking an image of the comet, which was of about magnitude 14.5, showing a faint tail in p.a. 150°. Additional images of the comet by various observers during the following days showed a 14.0-14.5 mag object with a 1.5' coma and a 1.5' long tail in southeastern direction. H. Sato was the first to notice the similarity to the orbit of asteroidal object 2018 HT3, discovered by NEOWISE in April 2018. Eventually, the object was detected in images as far back as 2012. With an orbital period of 5.13 years comet P/2018 HT3 (NEOWISE) passed perihelion on March 29, 2023 at the solar distance of only 0.52 AU with a proposed magnitude of 14.0 (CBET 5252). It should become fainter than 16 mag towards the end of May 2023, but will then be positioned low in the Southern Sky. From central European locations it could only be observed until around March 20 in the evening sky.
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Comet 71P/Clark (P=5.56a) passed perihelion at the solar distance of 1.59 AU on Jan. 22, 2023, but was then positioned too close to the Sun. In April 2023 the comet was observed as an object of about magnitude 13.0, showing a diffuse (DC 3) coma of diameter 1.5'. Thus it was a half to a full magnitude fainter than predicted.
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Comet 77P/Longmore (P=6.90a) will pass perihelion in the solar distance of 2.35 AU on Apr. 3, 2023, expected to peak at magnitude 13. During winter 2022/23 it moves from northwestern Virgo towards the border to Libra, and then until perihelion into the southeastern part of Hydra.
Based on 53 observations from 13 observers a brightness development is shown which is on the one hand time-dependent, on the other hand shows an increase in activity up to 35 days after perihelion passage and finally reveals clear differences pre- and post-perihelion. The corresponding formulas are as follows:
t < +35d: m = 13.7 mag + 5×log D – 0.015×(t-T)
t > +35d: m = 13.0 mag + 5×log D + 0.005×(t-T)
The peak brightness of 13.9 mag was reached at the opening of May 2023. The coma diameter increased steadily from 0.6' (35,000 km) at the start of the apparition to the maximum of 0.8' (50,000 km) around perihelion, but decreased thereafter, measuring just 0.4' (25,000 km) in mid-July. The coma was significantly condensed (DC 4-5). Very few tail observations have been reported.
Total Brightness and Coma Diameter
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The short-period comet 96P/Machholz (P=5.33a) passed perihelion on Jan. 31, 2023 at the solar distance of only 0.12 AU. The passage could be followed via SOHO. The comet displayed a prominent short tail. This comet is always a very difficult object, because it is near the Sun when bright, fading rapidly during the following days/weeks.
At this passage an attempt was made to extract the brightness from the SOHO images. In addition, a dozen terrestrial observations were published, covering the period Feb. 6 to Mar. 28. Based on the total of 30 observations from 6 observers the brightness development can be well described by the parameters
m0 = 12.2 mag / n = 5.2
yielding a maximum brightness of about 0 mag at perihelion. Until the beginning of March the comet had faded below 16 mag. The terrestrially observed coma diameter reached a maximum of 2' (95,000 km), decreasing to 1' (65,000 km) until the end of March. Estimates of the degree of condensation have not been published.
Total Brightness and Coma Diameter
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At the opening of July 2023 the number of published observations of comet 185P/Petriew (P=5.46a) is very small, a consequence of the fact that the comet was at small elongations around perihelion (on July 12 at the distance of 0.93 AU). The comet peaked at about magnitude 13.0 around perihelion. At mid-European locations the comet could not be observed in a reasonable way.
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On its way to its perihelion (taking place on May 14, 2023 at the solar distance of 0.80 AU) comet 364P/PANSTARRS (P=4.89a) will approach Earth to within 0.121 AU on Apr. 8, expected to reach magnitude 10.5. Thus this will be a favorable morning apparition. The comet should get brighter than 16 mag at the start of March, then moving through the constellation Bootes, being situated at high altitudes. At the start of April, 11-12 mag bright and moving through Hercules, it will reach maximum altitude. Thereafter it rapidly sinks towards the horizon and will disappear between Apr. 15 and 20 (at 11.0 mag) above the eastern morning horizon.
This comet was observed for only two months. On the basis of only 37 observations from 20 observers, which show a noticeable scatter, only a preliminary analysis can be performed. The comet is a rather small body with a surprisingly high activity. The brightness development can be simulated moderately well with the following parameters
Total Brightness and Coma Diameter
Andreas Kammerer
pre-perihelion: m0 ≈ 16.5 mag / n = 9
post-perihelion: m0 ≈ 14.7 mag / n = 2
Thus, the activity increased very rapidly pre-perihelion and decreased very slowly post-perihelion. The maximum brightness of 11.5 mag was reached on Apr. 13, 2023, and was about one magnitude below the predictions. The apparent coma diameter increased from 0.3' in early March to the short-term maximum of 1.2' around Apr. 20, then decreased to 0.8' by early May. The absolute coma diameter increased from only 5,000 km to 10,000 km during the same period. Estimates of the degree of condensation vary widely, with mean values of DC 4...5. Tail sightings have been reported throughout the apparition with maximum values of 5' (50,000 km). The tail was initially directed towards West, but slowly turned towards Southwest.
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