Comet Chasing

September offers two comets visible in small telescopes.

C/2020 F3 (NEOWISE) passed perihelion in early July. In late July this comet passed within 0.7 AU of the earth. Although this comet has lost its former glory, it is still the brightest comet in the sky, visible in small telescopes.

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 K8 (Catalina-ATLAS) will reach perihelion on September 14. It is predicted to obtain maximum brightness of magnitude 13 in early September.

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 12.7 in late June.

C/2020 F8 (SWAN) was discovered on SWAN images on April 9. It passed perihelion on May 26 and in late May it passed within 0.8 AU of the earth. It is currently a naked-eye object..

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

58P/Jackson-Neujmion passed perihelion in late May.

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

C/2019 Y1 (ATLAS) passed perihelion in March.

C/2018 F4 (PANSTARRS) passed perihelion last December.

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!

C/2020 K8 (Catalina-ATLAS): A morning comet visible in very large telescopes
This comet begins the month in Cancer at magnitude 13.2. Look for a 55" coma. It should fade rapidly, moving into Leo by month's end. FINDER CHART

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	Very low in the eastern sky during morning twilight at ~03:20	Not visible	Not visible	Not visible	Not visible	1-1
40^o N	Low in the eastern sky during morning twilight at ~04:00	Very low in the eastern sky during morning twilight at ~04:30	Very low in the eastern sky during morning twilight at ~04:40	Not visible	Not visible	1-13
Equator	Low in the eastern sky during morning twilight at ~04:50	Low in the eastern sky during morning twilight at ~05:00	Low in the eastern sky during morning twilight at ~04:50	Very low in the eastern sky during morning twilight at ~04:50	Not visible	1-25
30^oS	Low in the eastern sky during morning twilight at ~05:00	Low in the eastern sky during morning twilight at ~05:10	Very low in the eastern sky during morning twilight at ~04:50	Very low in the eastern sky during morning twilight at ~04:50	Not visible	1-23

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	Low in the western sky during evening twilight at ~20:20	Very low in the western sky during evening twilight at ~20:00	Very low in the western sky during evening twilight at ~19:40	Very low in the western sky during evening twilight at ~19:10	Very low in the western sky during evening twilight at ~18:50	1-
40^o N	Fairly high in the western sky during evening twilight at ~19:40	Low in the western sky during evening twilight at ~19:40	Low in the western sky during evening twilight at ~19:30	Low in the western sky during evening twilight at ~19:10	Low in the western sky during evening twilight at ~18:50	1-
Equator	High during evening twilight at ~19:00	Fairly high during evening twilight at ~19:10	Fairly high during evening twilight at ~19:00	Fairly high in the western sky during evening twilight at ~19:00	Fairly high in the western sky during evening twilight at ~18:50	1-
30^oS	Fairly high during evening twilight at ~18:50	Fairly high during evening twilight at ~19:00	Fairly high during evening twilight at ~19:00	Fairly high in the western sky during evening twilight at ~19:10	Fairly high in the western sky during evening twilight at ~19:00	1-

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	Fairly high during evening twilight at ~20:50	Fairly high during evening twilight at ~20:10	Fairly high at ~20:30	Fairly high at ~20:10	Fairly high during evening twilight at ~19:30	1-
40^o N	High during evening twilight at ~20:00	High at ~20:00	High at ~19:50	High at ~19:40	High during evening twilight at ~19:10	1-
Equator	High during evening twilight at ~19:10	High at ~19:20	High at ~19:10	Fairly high in moonlight at ~19:10	Fairly high during evening twilight at ~19:00	1-
30^oS	Fairly high in the northern sky during evening twilight at ~18:50	Fairly high in the northern sky at ~19:10	Fairly high in the northern sky during evening twilight at ~19:10	Fairly high in the western sky during evening twilight at ~19:10	Low in the western sky during evening twilight at ~19:00	1-

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	Low in the western sky during evening twilight at ~20:30	Low in the western sky during evening twilight at ~20:10	Very low in the western sky during evening twilight at ~20:00	Very low in the western sky during evening twilight at ~19:40	Very low in the western sky during evening twilight at ~19:00	1-29
40^o N	Fairly high in the western sky during evening twilight at ~19:50	Low in the western sky during evening twilight at ~19:50	Low in the western sky during evening twilight at ~19:40	Low in the western sky during evening twilight at ~19:20	Low in the western sky during evening twilight at ~19:00	1-
Equator	Fairly high during evening twilight at ~19:00	Fairly high at ~19:10	Fairly high in the western sky at ~19:10	Fairly high in the western sky in moonlight at ~19:10	Fairly high in the western sky during evening twilight at ~18:50	1-
30^oS	Fairly high during evening twilight at ~18:50	Fairly high in the western sky at ~19:10	Fairly high in the western sky during evening twilight at ~19:10	Fairly high in the western sky during evening twilight at ~19:10	Fairly high in the western sky during evening twilight at ~19:00	1-

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	High at ~02:30	High during morning twilight at ~03:20	High in moonlight at ~03:00	High at ~02:50	High at ~02:30	1-
40^o N	High at ~03:30	High in moonlight at ~04:00	High at ~00:40	High at ~03:00	High at ~02:30	1-
Equator	High at ~04:20	High in moonlight at ~04:00	High at ~02:10	High at ~02:50	High at ~02:30	1-
30^oS	Fairly high at ~04:40	Fairly high in moonlight at ~04:00	Fairly high at ~03:10	Fairly high at ~03:00	Fairly high at ~03:20	1-

Latitude	Visibility August 29	Visibility September 5	Visibility September 12	Visibility September 19	Visibility September 26	Nights Visible
55^o N	High at ~02:40	High during morning twilight at ~03:20	High in moonlight at ~03:10	High at ~02:20	High at ~00:10	1-
40^o N	High at ~03:40	High during morning twilight at ~04:10	High in moonlight at ~03:50	High at ~02:20	High at ~01:10	1-
Equator	High at ~04:40	High during morning twilight at ~04:50	Fairly high in moonlight at ~04:30	Fairly high in the northern sky at ~02:20	Low in the northern sky at ~02:30	1-
30^oS	Low in the northern sky during morning twilight at ~05:00	Low in the northern sky during morning twilight at ~05:10	Not visible	Not visible	Not visible	1-11

Comet	Constellation	September 1st		September 15th		September 30th		Observations as of (UT)
Comet	Constellation	Mag	Diam	Mag	Diam	Mag	Diam	Observations as of (UT)
C/2020 F3 (NEOWISE)	Virgo	8.7	4.4'	10.0	3.5'	11.1	2.9'	2020 August 25
88P/Howell	Libra	9.5	4.0'	9.5	3.9'	9.5	3.8'	2020 August 24
C/2019 N1 (ATLAS)	Coma Berenices	10.3	5.0'	10.1	5.0'	9.9	5.1'	2020 August 13
C/2019 U6 (Lemmon)	Bootes	11.4	2.6'	12.1	2.3'	12.9	2.0'	2020 August 24
C/2017 T2 (PANSTARRS)	Virgo	12.1	1.5'	12.5	1.4'	12.9	1.3'	2020 August 24
2P/Encke	Lupus	12.9	59"	14.3	46"	15.5	37"	2020 August 28
29P/Schwassmann-Wachmann	Aries	13.0	1.2'	12.9	1.3'	12.8	1.3'	2020 August 25
C/2020 K8 (Catalina-ATLAS)	Cancer	13.2	1.2'	13.3	51"	14.7	39"	2020 August 21
C/2020 Q1 (Borisov)	Auriga	13.7	1.2'	13.2	1.6'	13.3	1.7'	2020 August 25
246P/NEAT	Virgo	14.2	44"	14.2	43"	14.2	42"	2020 July 10
C/2018 N2 (ASASSN)	Ursa Minor	14.3	45"	14.4	44"	14.5	43"	2020 August 21
C/2017 K2 (PANSTARRS)	Hercules	14.6	22"	14.5	22"	14.4	22"	2020 August 25
C/2019 L3 (ATLAS)	Cassiopeia	15.0	22"	14.8	23"	14.7	24"	2020 August 21