Comet Chasing in September Comet chasing is the visual observation of telescopic comets. News

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 T his comet has o utbursts, 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.

Comet Visibility in the Eyepiece

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!

Comet Synopses for September Explanation of Comet Synopses and charts (read this if you have questions) C/2020 F3 (NEOWISE): An evening comet visible in small telescopes

This comet begins the month in Virgo at magnitude 8.7. Look for a 4' coma. It should fade rapidly, moving into Libra 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 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 o S 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- 88P/Howell: An evening comet visible in small telescopes

This comet begins the month in Libra at magnitude 9.5. Look for a 4' coma. It should remain constant, moving into Scorpius by month's end. The best visibility is mid-month as seen from the southern hemisphere. FINDER CHART Latitude Visibility August 29 Visibility September 5 Visibility September 12 Visibility September 19 Visibility September 26 Nights Visible 55 o N Not visible Not visible Not visible Not visible Not visible 40 o N Low in the western sky during evening twilight at ~19:40 Low in the western sky during evening twilight at ~19:50 Low in the western sky during evening twilight at ~19:30 Low in the southern sky during evening twilight at ~19:20 Low in the southern sky during evening twilight at ~19:00 1- Equator High during evening twilight at ~19:00 High at ~19:10 High at ~19:10 High in moonlight at ~19:10 High during evening twilight at ~19:00 1- 30 o S High during evening twilight at ~18:50 High at ~19:10 High at ~19:20 High in moonlight at ~19:20 High during evening twilight at ~19:10 1- C/2019 U6 (Lemmon): An evening comet visible in a 10-inch (25 cm) telescope

This comet begins the month in Bootes at magnitude 11.4. Look for a 2.5' coma. It should fade by about 1.5 magnitudes, moving into Hercules 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 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 o S 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- C/2017 T2 (PANSTARRS): An evening comet visible in a 12.5-inch (32 cm) telescope

This comet begins the month in Virgo at magnitude 12.1. Look for a 1.5' coma. It should fade by about 0.9 magnitudes, moving into Libra 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 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 o S 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- 29P/Schwassmann-Wachmann: A morning comet visible in a 16-inch (41 cm) telescope

This comet begins the month in Aries at magnitude 13.0. Look for a 1.5' coma. It should brighten slowly. FINDER CHART 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 o S 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- C/2020 Q1 (Borisov): A morning comet visible in a 16-inch (41 cm) telescope

This comet begins the month in Auriga at magnitude 13.7. Look for a 1.5' coma. It should brighten slowly, moving into Cepheus 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 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 o S 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 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 o S 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

Summary Data for This Month's Telescopic Comets

C

omets brighter than 15th magnitude. This table is updated as necessary. The last column indicates the date of the last observation used to compute these values. The constellation listed is where the comet was on the first of the month.

Comet Constellation September 1st September 15th September 30th Observations as of (UT) Mag Diam Mag Diam Mag Diam 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

*In solar conjunction and generally not visible

For information about specific comets see Gary W. Kronk's Cometography

Further reading: see Comet Chasing, Sky & Telescope, April 2005, pg. 83.

Make your own custom charts for your location and telescope/binoculars: software for visual comet observing