Comet Chasing

September offers two comets visible in small telescopes.

156P/Russell-LINEAR is brighteing rapidly and unexpectedly. As of October 15, this comet has brightened by several magnitudes to approximately magnitude 11.8, and may continue to brighten in the coming days/weeks. This comet will next reach perihelion in mid November, when it will also be within 0.5 AU of the earth.

C/2020 M3 (ATLAS) will next reach perihelion in late October. On October 25, this comet will pass within 0.4 AU of the earth. It is currently predicted to attain maximum brightness of magnitude 8.2 in early November.

C/2020 P1 (NEOWISE) will reach perihelion on October 20. In mid October this comet will pass within 0.7 AU of the earth, when It also is predicted to reach maximum brightness of magnitude 8.

88P/Howell will reach perihelion in late September. It is predicted to reach maximum brightness of magnitude 9.5 in mid September

C/2020 Q1 (Borisov) passed perihelion in mid August. In late September this comet will pass within 0.7 AU of the earth. It is predicted to reach maximum brightness of magnitude 13 in late September.

C/2020 F3 (NEOWISE) was a Great Comet that passed perihelion in early July. In late July this comet passed within 0.7 AU of the earth.

C/2020 K8 (Catalina-ATLAS) apparently faded significantly after perihelion on September 14 and appears to no longer be observable.

A/2019 U6 (Lemmon). This former asteroid was observed to have a cometary coma in early February, apparently noted by A. Novichonok. It passed perihelion on June 18.

C/2017 T2 (PANSTARRS) passed perihelion in early May.

C/2019 N1 (ATLAS) will reach perihelion in early December. It is currently predicted to reach a maximum brightness of magnitude 9.7 in early January 2021.

246P/NEAT will next reach perihelion in late February 2021. It is currently predicted to reach maximum brightness of magnitude 13.5 in late June of 2021..

2P/Encke passed perihelion on June 25. In late July this comet passed within 0.6 AU of the earth.

C/2017 T2 (PANSTARRS): passed perihelion in early May.

C/2019 Y4 (ATLAS). This comet had the potential to become a bright naked-eye object near perihelion in late May, but on April 8 it was observed in images to have fragmented. It has not been observed since late May and is presumed lost.

2I/Borisov (formerly C/2019 Q4) is the first interstellar comet, discovered on August 30, 2019 by G. Borisov. It took until September 10/11 for the interstellar nature of this comet to become readily apparent. On September 24 the IAU officially recognized it as interstellar and assigned a new designation. It will reach perihelion in early December, when it will come within 1.9 AU of the sun and earth. At that time it will be in Hydra. It isn't yet clear how bright it will become, but with comets there is always the possibility that it will brighten enough to be observable visually in large instruments. More here...

29P/Schwassmann-Wachmann This comet has outbursts, resulting in a brightening of 0.5 - 1.0 magnitudes, which occur roughly every 59 days, typically taking 5-10 days to subside. Up to three subsequent outbursts may occur 5-10 days afterward, each typically smaller than the last, although on some occasions they can be even brighter than the first. These outbursts make 29P one of the most interesting comets to follow, both visually and scientifically. 29P/Schwassmann-Wachmann has a 14.8-year orbital period, and last passed perihelion in early March 2019. It varies in its distance from the Sun from 5.8 AU (at perihelion) to 6.3 AU (at aphelion), which is an unusually small variation for a comet, and remains quite far from the sun at all times. This means that it can be observed more or less continuously.

C/2020 F3 (NEOWISE) on the evening of July 29, in moonlight, from Cloudcroft, New Mexcio.

This page uses code developed for SkyTools to predict the visibility of a comet in the eyepiece. Predicting how much aperture is required to see a comet is a very complex task. Have a look for yourself: a comparison of the predictions below (such as "visible in small telescopes") to the magnitude of each comet shows just how poor an indicator the magnitude alone really is. When you read below that a particular aperture is required to see a comet you can have a reasonable degree of confidence that the comet can in fact be seen in the eyepiece. But always remember, comets are like cats. They both have tails and do what they want, and not always what we expect. This is one of the things that makes comet chasing interesting!

29P/Schwassmann-Wachmann: A morning comet visible in very large telescopes
This comet begins the month in Aries at magnitude 13.0. Look for a 3' coma. It should remain constant. FINDER CHART

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	High in moonlight at ~02:00	High at ~22:20	High at ~00:50	High at ~00:20	High in moonlight at ~23:40	1-
40^o N	High in moonlight at ~02:00	High at ~23:30	High at ~00:50	High at ~00:20	High in moonlight at ~23:40	1-
Equator	High in moonlight at ~02:00	High at ~00:50	High at ~00:50	High at ~01:20	High in moonlight at ~23:50	1-
30^oS	Fairly high in moonlight at ~02:00	Fairly high at ~01:30	Fairly high at ~00:50	Fairly high in the northern sky at ~02:00	Fairly high in moonlight at ~23:50	1-

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	Not visible	Very low in the southern sky in moonlight at ~03:30	Low in the southern sky at ~03:10	Low in the southern sky at ~02:50	Fairly high in the southern sky in moonlight at ~02:40	1-
40^o N	Low in the southern sky in moonlight at ~03:40	Fairly high in the southern sky in moonlight at ~03:30	Fairly high in the southern sky at ~03:10	Fairly high at ~02:50	Fairly high in moonlight at ~02:40	1-
Equator	High in moonlight at ~03:40	High at ~00:50	High at ~03:10	High at ~02:50	High in moonlight at ~02:40	1-
30^oS	High in moonlight at ~03:40	High at ~01:50	High at ~03:10	High at ~02:50	High in moonlight at ~02:40	1-

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	Not visible	Not visible	Not visible	Not visible	Not visible	1-
40^o N	Low in the southern sky during evening twilight at ~18:50	Low in the southern sky during evening twilight at ~18:50	Low in the southern sky during evening twilight at ~18:40	Low in the southern sky during evening twilight at ~18:20	Low in the southern sky during evening twilight at ~18:10	1-
Equator	Fairly high at ~19:10	Fairly high at ~19:00	Fairly high at ~19:00	High during evening twilight at ~18:50	High during evening twilight at ~18:50	1-
30^oS	High at ~19:30	High at ~19:30	High at ~19:40	High during evening twilight at ~19:30	High during evening twilight at ~19:30	1-

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	Not visible	Not visible	Not visible	Very low in the eastern sky during morning twilight at ~05:10	Low in the eastern sky during morning twilight at ~05:30	18-
40^o N	Not visible	Not visible	Not visible	Very low in the eastern sky during morning twilight at ~05:10	Low in the eastern sky during morning twilight at ~05:20	17-
Equator	Not visible	Not visible	Not visible	Not visible	Not visible	16-
30^oS	Very low in the eastern sky during morning twilight at ~04:40	Very low in the eastern sky during morning twilight at ~04:40	Not visible	Not visible	Not visible	1-15

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	Very low in the western sky during evening twilight at ~18:30	Not visible	Not visible	Not visible	Not visible	1-9
40^o N	Very low in the western sky during evening twilight at ~18:40	Very low in the western sky during evening twilight at ~18:30	Very low in the western sky during evening twilight at ~18:10	Not visible	Not visible	1-23, 25-25
Equator	Fairly high in the western sky during evening twilight at ~18:50	Low in the western sky during evening twilight at ~18:50	Low in the western sky during evening twilight at ~18:40	Very low in the western sky during evening twilight at ~18:40	Not visible	1-
30^oS	Fairly high in the western sky during evening twilight at ~19:10	Low in the western sky during evening twilight at ~19:10	Low in the western sky during evening twilight at ~19:20	Very low in the western sky during evening twilight at ~19:10	Not visible	1-

Latitude	Visibility October 3	Visibility October 10	Visibility October 17	Visibility October 24	Visibility October 31	Nights Visible
55^o N	Not visible	Very low in the southern sky at ~22:20	Low in the southern sky at ~21:50	Low in the southern sky at ~23:10	Fairly high in the southern sky in moonlight at ~20:50	4-
40^o N	Low in the southern sky in moonlight at ~23:00	Fairly high in the southern sky at ~22:20	Fairly high in the southern sky at ~21:50	Low in the southern sky at ~00:10	Fairly high in moonlight at ~21:00	1-
Equator	Fairly high in the eastern sky at ~19:10	High at ~22:20	High at ~21:50	Fairly high in the western sky at ~01:20	High in moonlight at ~21:00	1-
30^oS	High at ~19:30	High at ~22:20	High at ~21:50	Fairly high in the western sky at ~02:00	High in moonlight at ~21:00	1-

Comet	Constellation	October 1st		October 15th		October 31st		Observations as of (UT)
Comet	Constellation	Mag	Diam	Mag	Diam	Mag	Diam	Observations as of (UT)
88P/Howell	Ophiuchus	8.9	2.4'	9.0	2.4'	9.3	2.2'	2020 September 21
C/2020 M3 (ATLAS)	Eridanus	9.1	7.7'	8.7	8.8'	8.3	10.4'	2020 September 26
C/2020 P1 (NEOWISE)	Centaurus	9.7	2.1'	8.1	2.3'	9.8	1.5'	2020 October 2
C/2017 T2 (PANSTARRS)	Libra	10.9	5.2'	11.2	5.0'	11.6	4.6'	2020 September 10
156P/Russell-LINEAR	Sculptor	11.7?	3.1?	11.7	3.1	11.6?	3.1?	2020 October 11
C/2020 F3 (NEOWISE)	Libra	11.4	2.7'	12.0	2.4'	12.8	2.1'	2020 September 22
C/2019 N1 (ATLAS)	Virgo	12.7	2.9'	12.5	3.0'	12.3	3.1'	2020 August 22
C/2019 U6 (Lemmon)	Hercules	12.8	5.5'	13.3	5.1'	13.9	4.6'	2020 October 1
29P/Schwassmann-Wachmann	Aries	13.0	2.9'	12.9	2.9'	12.9	2.9'	2020 September 24
C/2020 Q1 (Borisov)	Cygnus	14.1	1.7'	14.8	1.3'	16.0	56"	2020 September 20
C/2018 F4 (PANSTARRS)	Fornax	14.6	60"	14.7	59"	14.8	57"	2020 September 20
C/2019 L3 (ATLAS)	Cassiopeia	14.8	1.3'	14.7	1.3'	14.5	1.4'	2020 October 1
C/2018 N2 (ASASSN)	Ursa Minor	14.8	31"	14.9	31"	15.0	31"	2020 September 22
246P/NEAT	Virgo	15?	42"?	15?	42"?	15?	42"?	2020 July 16
C/2020 F5 (MASTER)	Apus	15.0	30"	15.0	30"	15.1	29"	2020 August 29
2P/Encke	Scorpius	15.1	2.8'	15.7	2.5'	16.5	2.1'	2020 September 5
C/2020 K8 (Catalina-ATLAS)	Leo	15.2	37"	16.3	32"	17.6	28"	2020 August 21
115P/Maury	Sagittarius	15.2	1.9'	15.5	1.8'	15.8	1.6'	2020 September 16
C/2017 K2 (PANSTARRS)	Hercules	15.3	1.3'	15.2	1.3'	15.2	1.3'	2020 October 1
C/2020 J1 (SONEAR)	Ara	15.4	58"	15.4	56"	15.5	53"	2020 September 21
C/2017 B3 (LINEAR)	Pisces	15.6	20"	15.7	20"	15.8	19"	2020 September 23
C/2019 T2 (Lemmon)	Capricornus	15.6	14"	15.6	13"	15.7	12"	2020 August 21
C/2017 Y2 (PANSTARRS)	Ophiuchus	15.7	20"	15.7	19"	15.8	19"	2020 September 10
84P/Giclas	Gemini	15.7	1.0'	15.8	1.1'	16.0	1.1'	2020 September 19