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On Oct. 31, 2010 A. Boattini discovered a 20.0 mag comet with the 1.5m-Mt.Lemmon-reflector near the border of the constellations Cetus/Aries. Comet C/2010 U3 (Boattini) showed a medium condensed 6-7" coma, elongated in p.a. 330°, harboring a 3-4" central condensation. Additional observations showed a 20" coma and a 25" tail in p.a. 330°. At discovery the comet stood in the record solar distance of 18.5 AU! It will not reach perihelion before Feb. 26, 2019 at a distance of 8.44 AU. Nevertheless it could become as bright as 15 mag, then moving through far-northern regions (Camelopardalis, Ursa Major, Draco) (IAUC 9182 / 2010-V109). This implies an inherently bright comet which showed a coma diameter of already 250.000 km at discovery!
An analysis of the apparition, based on only two dozen observations, yields the brightness parameters m0=6.7 mag / n=2. Thus the comet peaked at magnitude 15.8 at the time of perihelion. Throughout the apparition the comet showed a constant coma diameter of about 0.4-0.5' (about 150.000 km).
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In the course of the LINEAR Sky Survey an asteroidal object of magnitude 19.5 was discovered on images taken on Jan. 26, 2017 near the border of the constellations Hydra/Corvus. Follow-up observations of comet C/2017 B3 (LINEAR) showed a significantly condensed 8" coma of total brightness 18.5 mag. This comet will pass perihelion on Feb. 2, 2019 at the distance of 3.92 AU, expected to peak around magnitude 14-15 (CBET 4354). However, at this time it will be positioned in the far Southern Sky. It will not be observable from mid-European locations during the time interval when it is expected to be brighter than 16.0 mag.
Because the comet was in conjunction with the Sun at perihelion the broad maximum brightness was reached in July/August 2019. According to 35 observations the comet showed a quite continuous brightness development which can be well described by the parameters m0=8.3 mag / n=2, which yield a maximum brightness of 14.2 mag. It showed a moderately condensed (DC 5) coma with the maximum diameter at 0.8' (100.000 km).
Total Brightness and Coma Diameter
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On images taken with the "Asteroid Terrestrial-impact Last Alert System" (ATLAS) on Jan. 10, 2018 an asteroidal object was discovered in the northern part of Virgo. Follow-up observations revealed its cometary nature. Comet C/2018 A3 (ATLAS) showed an 8" coma of total magnitude 18.0. It will pass perihelion in the solar distance of 3.28 AU on Jan. 11, 2019, expected to peak at magnitude 15.0 (CBET 4476 / MPEC 2018-B155). It should be brighter than magnitude 16.0 between November 2018 and February 2019, thereby moving from the central part of Ursa Mayor to the southwestern part of Camelopardalis, thus being observable for mid-European observers during the whole night.
Only a small number of observations had been published. These indicate a maximum brightness of 15.0-15.5 mag in January 2019 with the coma measuring about 0.7'. The brightness parameters are about m0=8.0 mag / n=4.
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On Jan. 15, 2018 A.R. Gibbs discovered a 19 mag comet in Leo. Follow-up observations of comet C/2018 A6 (Gibbs) showed a highly condensed, 10" coma of total magnitude 18.8 and a fan-shaped 15" tail (PW=110-17°). The comet will pass perihelion in the solar distance of 3.02 AU on July 14, 2019, expected to peak at magnitude 15 (CBET 4479). However, after the start of 2019 (then 16.0 mag) it will be situated far in the southern sky.
According to 41 observations from 5 observers the comet showed a significant difference in the brightness development pre- and post-perihelion, which can be well described by the formulae
pre-perihelion: m = 3.8 mag + 5×log D + 16×log r post-perihelion: m = 9.0 mag + 5×log D + 5×log rThus the comet experienced the maximum brightness of 13.9 mag during many weeks around the perihelion date. At the start and the end of the apparition the coma measured 0.45' (60.000 km / 75.000 km), peaking at 0.7' (110.000 km) in fall 2019. During the whole apparition the coma was rather diffuse (constant at DC 3).
Total Brightness and Coma Diameter
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On images taken with the Mt.Lemmon reflector already on Feb. 25, 2018 an asteroidal object of magnitude 21.5 was discovered in Coma Berenice. Observations starting at the end of August 2019 noticed cometary activity on the object. At the start of September comet C/2018 DO4 (Lemmon) showed a 20" coma of total magnitude 16.5 and a 45" tail, pointing towards NW. At the opening of October the significantly condensed 15" coma was of total magnitude 16.0, and a 70" tail was pointing towards NW (CBET 4675). The comet, with an orbital period of about 130 years, passed perihelion on Aug. 18, 2019 in the distance of 2.41 AU. At the end of October – positoned in the southwest corner of Taurus - it peaked at magnitude 15.5, displaying a coma of diameter 0.5'.
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Comet C/2018 W1 (CATALINA), which was discovered by the CATALINA team on Nov. 16, 2018 in the eastern part of Andromeda and passed its perihelion on May 11, 2019 at a solar distance of 1.36 AU, surprised the observers in the southern hemisphere in a very positive way. Based on the discovery magnitude of 19.0 and assuming a standard development (n=4) a maximum brightness of 16.0 mag was predicted.
However, the comet reached a maximum brightness of 11.5 mag in May 2019! The brightness parameters, derived from only a small number of observations, are m0=7.5 mag / n=8, indicating that the comet had been brighter than 16.0 mag between January and August 2019. In May 2019 it showed a moderately condensed (DC 3) coma of diameter 2.5' (190.000 km).
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On Feb. 26, 2019 Heather Flewelling discovered a comet in the constellation Scutum in the course of the "Asteroid Terrestrial-Impact Last Alert System" (ATLAS). Comet C/2019 D1 (Flewelling) was of magnitude 15.5, showing a highly condensed, 20" coma and a 1.5' tail in p.a. 260°. It will pass perihelion in the solar distance of 1.58 AU on May 11, 2019, expected to reach magnitude 14 (CBET 4614). It should have faded to magnitude 16 at the end of September. During this period it should move through the constellations Aquila, Delphinus, Pegasus, eventually reaching Andromeda. Thus it will be an object in the morning sky.
A scant 25 observations allow only a rough analysis. According to these the brightness developed according to the parameters m0≈5.0 mag / n≈15, indicating a surprisingly rapid development. The maximum brightness of 13.5 mag was reached in May 2019 with the comet showing a well-condensed (DC 5) coma of about 0.7' (appx. 45.000 km) diameter.
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Quan-zhi Ye of the California Institute of Technology discovered a comet near the border of the constellations Andromeda/Cassiopeia on images taken with the 1.2m-Schmidt-telescope on Mt. Palomar Observatory on May 9, 2019. Comet C/2019 J2 (Palomar) showed a considerably condensed 8" coma of total magnitude 17.0 and a faint 20" tail pointing towards SW. The comet will reach perihelion on its 316 years orbit on July 19, 2019 at the solar distance of 1.73 AU, expected to reach 15.5 mag (CBET 4626/ MPEC 2019-O96).
Actually the comet peaked at magnitude 15.0 in mid-June 2019, showing a 1' coma. However, only a very small number of observations have been published. Then, at the opening of July, it began to disintegrate
(The Astronomer’s Telegram No. 12931).
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On images taken with the 0.65m astrograph of the Margo Observatory on Aug. 30, 2019, Gennady Borisov discovered a comet near the border of the constellations Lynx/Cancer. It displayed a 7" coma of total magnitude 18.0 and a 15" tail in p.a. 310°. Follow-up observations showed comet C/2019 Q4 (Borisov) with a significantly condensed 20" coma of total magnitude 17.5 and a 50" tail. In mid-September the comet showed a 18" coma of total magnitude 17.0 and a 100" tail in p.a. 309°. Only a few days after discovery it became clear that this is the first interstellar comet (with e=3.4!). The comet, which was named 2I/Borisov, will pass perihelion on Dec. 8 in the solar distance of 2.01 AU. Depending on the actual brightness development its peak brightness should be of magnitude 14.5 to 15.0 (CBET 4666/68/70). Thus it is possible to glimpse this comet with amateur telescopes! It should be brighter than 16.0 mag between November 2019 and January 2020. During this period it will move through the constellations Sextans, Crater, Hydra and Centaurus. From mid-European locations it will be observable in the morning sky until mid-December.
In mid-October the comet was of magnitude 16.0, showing a brighter 4" inner and a fainter 10" outer coma; a faint fan-like tail of 25" length was seen in p.a. 320°. On Oct. 10 H. Sato reported a CCD-brightness of 16.7 mag, a strongly condensed 15" coma and a 40" tail in p.a. 315° (CBET 4691).
Unfortunately the interstellar comet remained somewhat fainter than predicted. Based on 39 observations from 13 observers a perfectly average brightness development results, which is best described by the formula
m = 10.5 mag + 5×log D + 10×log rThis yields a maximum brightness of 15.0 mag in mid-December 2019, which resulted in a very small number of visual observations. Between mid-September 2019 and early January 2020 the apparent coma diameter varied not much, due to the quite large solar distance of the comet. It measured 0.35' at the beginning of the apparition, increased to its maximum value of 0.7' at the end of November and was estimated as 0.6' in early January. Taking into account the accuracy of the estimates, a constant absolute coma diameter of 60.000 km results. Estimates of the degree of condensation were rare with the observers reporting DC 3. On CCD-images a short tail, pointing towards Northwest, of length 2' (250.000 km) could be detected.
Professional CCD-observations recognized a small outburst of this comet at the start of March 2020. They measured a total magnitude of 17.0 mag and a coma diameter of 15" on Feb. 3 and magnitude 18.2 on Mar. 2. Between Mar. 7 and 10 the brightness increased 0.9 mag to 17.1 mag, but was measured 17.4 mag on Mar. 13 (CBET 4729).
Scheinbare Helligkeit und Komadurchmesser
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Comet 60P/Tsuchinshan (P=6.58a) will pass perihelion for another time on Dec. 11, 2018 in the solar distance of 1.62 AU. In November 2018 it should become brighter than 16 mag, brightening to 14.5 mag until mid-February 2019. The comet moves from the southwestern part of Leo towards the border of the constellations Virgo/Sextans, being visible in the morning sky.
For the analysis 70 observations from 21 international observers could be used. These yield a brightness development according to the formula
m = 12.5m + 5×log D + 5×log rConsidering that this comet is an old periodic one the derived activity parameter is unusually small. The comet peaked at 13.3 mag in mid-February 2019. Due to the approach to Earth until the end of February the apparent brightness increased more slowly during the first weeks, fading significantly more rapid thereafter. The apparent coma diameter increased continuously from 0.4' at the start of the apparition to the maximum of 1.1' at the end of February 2019. Thereafter it decreased, reaching 0.6' at the end of May. Contrary, the absolute coma diameter remained rather constant between 40.000 and 45.000 km. The degree of condensation was DC 4 at the start of the apparition, increasing to DC 5 until the opening of February 2019. Thereafter it decreased, reaching DC 2-3 at the start of April. A tail, pointing constantly towards NW, was observed between mid-November 2018 and end of February 2019, reaching up to 5' (500.000 km).
Total Brightness and Coma Diameter
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On Nov. 9, 2019 comet 68P/Klemola (P=11.0a) will pass perihelion at the distance of 1.79 AU for an additional time. It should be brighter than 16 mag between May 2019 and February 2020. During this interval it will move along the ecliptic from Ophiuchus towards the border of the constellations Aquarius/Pisces. For mid-European locations it will thus be observable above the evening horizon at rather low altitudes.
In spite of a maximum brightness of only 13.4 mag (around Oct. 10, 2019) 45 observations from 16 observers could be used for the analysis. The brightness development can be rather well represented by the parameters m0=7.1 mag / n=8. Thus the comet showed an high activity parameter, which is typical for an old periodic comet. At the opening of the apparition at short of 1.0' (60.000 km) the coma diameter increased steadily, reaching a maximum of 1.4' (90.000 km) at the end of August. Thereafter it decreased, reaching 0.6' (45.000 km) at the start of November. During the apparition the degree of condensation decreased from DC 4 to DC 3. A miniscule tail could be detected by CCD-observers between June and August. It changed orientation from SW towards SE.
Total Brightness and Coma Diameter
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Comet 78P/Gehrels (P=7.23a) can be observed during winter 2018/19, reaching perihelion on Apr. 2, 2019 at the solar distance of 2.01 AU. However, at this time it will be situated too near the Sun for observations. For mid-European observers it will be situated low above the evening horizon during winter 2018/19, moving from the northeastern part of Capricornus towards the border of the constellations Pisces/Cetus. It should brighten from magnitude 13.5 to 13.0.
Based on 42 observations from 11 observers the apparition 2018-20 of this comet can be analysed. These are not well distributed in time, with a larger number dated between August 2018 and January 2019 and between December 2019 and February 2020. During these two intervals the comet was placed too near the Sun to be observable. The observations can be described by the brightness parameters m0=8.2 mag / n=4.5, yielding a broad maximum of 13.8 mag between October 2018 and February 2019. However, it is possible that the comet actually showed a different brightness development pre- and post-perihelion, which is not noticable due to the time gap. The coma measured about 1.0' (75.000 km) in the first period and 0.6' (55.000 km) in the second. The coma was rather diffuse (DC 3) throughout the apparition.
Total Brightness and Coma Diameter
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Comet 114P/Wiseman-Skiff (P=6.67a) will pass perihelion on Jan. 14, 2020 at the distance of 1.58 AU. According to current observations it should peak at 15.0 mag in December 2019. During winter 2019/20 it moves from Andromeda into Taurus, thus will be well placed in the evening sky.
The comet exhibited a surprisingly high level of activity during this apparition. Based on 45 observations from 17 observers the brightness developed according to the parameters m0=7.5 mag / n=14, yielding a maximum brightness of 13.9 mag around Christmas 2019. The coma diameter increased from 0.6' (25.000 km) at the start of the apparition to 1.1' (35.000 km) during the Christmas days, only to decrease to 0.5' (27.000 km) until mid-February 2020. The coma was moderately condensed (DC 3-4). CCD observers could detect a miniscule tail pointing eastward.
Total Brightness and Coma Diameter
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In autumn 2018 comet 123P/West-Hartley (P=7.58a) should become brighter than 16.0 mag. It will pass perihelion at the distance of 2.13 AU on Feb. 5, 2019, expected to reach magnitude 13. In winter 2018/19 it will make an opposition loop near the borders of the constellations Leo Minor/Leo/Ursa Major.
The development of the comet during this apparition has been analysed using 98 observations from 15 international observers. The brightness estimates can be well represented by the parameters m0=8.8 mag / n=4.5, yielding a maximum brightness of 12.9 mag at the end of February 2019. The apparent coma diameter increased from 0.8' at the start of the apparition to the maximum of 2.0' in mid-March. Thereafter it decreased, reaching 1.3' at the end of May. The absolute coma diameter increased from 55.000 km at the start of the apparition to the maximum of 110.000 km at the end of February. This value was then hold until the end of the apparition. Surprisingly, the coma grew ever more diffuse throughout the apparition; the degree of condensation decreased from DC 5-6 to DC 2. Very few observers reported a tail up to 2' (700.000 km) in February.
Total Brightness and Coma Diameter
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Comet 155P/Shoemaker (P=16.9a) should become observable in amateur telescopes in winter 2019/20. It reaches perihelion on Nov. 15, 2019 in the distance of 1.80 AU. According to current observations it should peak at 14.5 mag during the last days of 2019. Between October 2019 and January 2020 it moves eastward through the constellations Cancer and Leo, thus being well observable in the morning sky.
The apparition 2019/20 can be analysed on the basis of 35 observations from 11 observers. The brightness estimates can be well described by the parameters m0=10.5 mag / n=6, yielding a maximum brightness of 15.0 at the turn 2019/20. The diameter of the rather diffuse (DC 3) coma increased from 0.5' at the beginning of the apparition to 0.7' in January, and was constant at this value thereafter. This indicates a constant absolute coma diameter of 38.000 km. Between mid-December and mid-February a 3' tail, pointing towards WNW, could be glimpsed by CCD observers.
Total Brightness and Coma Diameter
Andreas Kammerer
