Comet Chasing in September

Comet chasing is the visual observation of telescopic comets.  Jump to:  Observing synopses    Summary data

News

There are two comets visible in small telescopes in September, but many more are visible in larger instruments.

  • C/2021 O1 (Nishimura) is a new discovery on July 21 by H. Nishimura. It was found very low in morning twilight. It was low in the sky throughout August, reaching magnitude 9 on August 12 (at perihelion of 0.8 AU), but was difficult to observe. By the time it is observable again after the beginning of the year it will lilkely have faded. 

  • C/2014 UN271 (Bernardinelli-Bernstein) is an interesting Oort cloud comet that was recently reported as a result of the Dark Energy Survey. Soon after it was made public, images showed a cometary coma. Discovery credit goes to Pedro Bernardinelli and Gary Bernstein. This is a remarkable comet that was at 29 AU in 2014, with a perihelion of 10.9 AU in 2031. Its orbit extends out to 40,000 AU! It is unusually bright for its distance, so it is either intrinsically bright or unusually large for a comet. Because of its distant perihelion, this comet is not expected to become bright enough to be visually observed except in large instruments, and not until the end of the decade, but it is likely going to be the subject of intense scientific scrutiny. 

  • C/2019 L3 (ATLAS) will reach perihelion on 2022 January 9, when it may be magnitude 11.

  • 4P/Faye will next reach perihelion in early September. It is currentlly predicted to reach maximum brightness of magnitude 11.5 in mid October.

  • 67P/Churyumov-Gerasimenko will next reach perihelion in early November. On November 2 this comet will pass within 0.4 AU of the earth when It is currently predicted to reach maximum brightness of magnitude 10.3. 

  • 15P/Finlay passed perihelion on July 13. 

  • 2020 T2 (Palomar) passed perihelion in mid July.  

  • 2020 J1 (SONEAR) passed perihelion in mid April.

  • C/2017 K2 (PANSTARRS) will reach perihelion in mid December 2022. It is predicted to reach maximum brightness of magnitude 6.5 in mid January 2023.

  • 6P/d'Arrest will next reach perihelion in mid September when it is predicted to reach maximum brightness of magnitude 10.8. 

  • 7P/Pons-Winnecke passed perihelion in late May. On May 27 this comet passed within 0.4 AU of the earth. It is currently predicted to reach maximum brightness of magnitude 11.2 in early June.

  • C/2020 R4 (Atlas) passed perihelion in early March. On March 1, this comet passed within 0.5 AU of the earth. This comet had an outburst in late April, brightening by as much as a magnitude. 

  • C/2021 A1 (Leonard) was discovered on January 3 by by G. J. Leonard at Mount Lemmon Observatory. It will reach perihelion on January 3, 2022. It may become visible to the naked eye in mid December 2021. It is currently very faint and not visualy observable. 

  • C/2021 A2 (NEOWISE) passed perihelion in late January. In early February this comet will pass within 0.5 AU of the earth. It is currently predicted to reach a maximum brightness of magnitude 11 in early February.

  • C/2021 A4 (NEOWISE) passed perihelion in mid-March.

  • 10P/Tempel passed perihelion in late March.

  • P/2016 J3 (STEREO) passed perihelion on January 25, when it passed within 0.5 AU of the earth. This comet unexpectedly returned early, based on the orbit that was calculated for it in 2016.

  • 246P/NEAT passed perihelion in late February 2021. It is currently predicted to reach maximum brightness of magnitude 14.7 in late June.

  • 29P/Schwassmann-Wachmann had an outburst on January 15. This comet has frequent 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.

Comets that have apparently disentegrated: C/2020 Q1 (Borisov), C/2020 P1 (NEOWISE), and C/2019 Y4 (ATLAS). Beware that various other online sources often fail to keep track of whether or not a comet still exists!

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!

Observing Synopses for September

Explanation of Comet Synopses and charts (read this if you have questions)

C/2019 L3 (ATLAS): A morning comet visible in small telescopes
This comet begins the month in Auriga at magnitude 10.0. Look for a 2' coma. It should brighten slowly.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N High during morning twilight at ~03:00 High during morning twilight at ~03:20 High during morning twilight at ~03:40 High during morning twilight at ~04:00 High in moonlight at ~04:00 1-
40o N High during morning twilight at ~04:00 High during morning twilight at ~04:10 High at ~04:10 High during morning twilight at ~04:30 High in moonlight at ~04:30 1-
Equator Fairly high in the northern sky during morning twilight at ~04:50 Fairly high during morning twilight at ~04:50 Fairly high during morning twilight at ~04:40 Fairly high during morning twilight at ~04:50 Fairly high during morning twilight at ~04:40 1-
30o S Not visible Not visible Very low in the northern sky during morning twilight at ~04:50 Very low in the northern sky during morning twilight at ~04:40 Low in the northern sky during morning twilight at ~04:30 1-

C/2020 T2 (Palomar): An evening comet visible in small telescopes
This comet begins the month in Libra at magnitude 10.5. Look for a 4' coma. It should fade by about 0.5 magnitudes, moving into Scorpius by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Low in the western sky during evening twilight at ~19:50 Low in the western sky during evening twilight at ~19:40 Not visible Not visible Not visible 1-
Equator High at ~19:10 High in moonlight at ~19:10 High during evening twilight at ~19:00 Fairly high at ~19:00 Fairly high at ~19:00 1-
30o S High at ~19:10 High in moonlight at ~19:10 High during evening twilight at ~19:10 High at ~19:20 Fairly high at ~19:20 1-

67P/Churyumov-Gerasimenko: A morning comet visible in a 6-inch (15 cm) telescope
This comet begins the month in Aries at magnitude 12.8. Look for a 1.5' coma. It should brighten by about 1.2 magnitudes, moving into Taurus by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N High at ~02:50 High at ~03:10 High at ~03:20 High during morning twilight at ~03:50 High in moonlight at ~03:50 1-
40o N High at ~03:50 High at ~03:50 High at ~04:00 High during morning twilight at ~04:20 High in moonlight at ~04:10 1-
Equator High at ~04:20 High at ~04:20 High at ~04:30 High during morning twilight at ~04:40 High in moonlight at ~04:10 1-
30o S High at ~04:20 High at ~04:20 High during morning twilight at ~04:40 Fairly high during morning twilight at ~04:30 Fairly high at ~04:10 1-

4P/Faye: A morning comet visible in an 8-inch (20 cm) telescope
This comet begins the month in Taurus at magnitude 11.9. Look for a 3.5' coma. It should brighten slowly, moving into Orion by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Fairly high during morning twilight at ~03:00 High at ~03:20 High at ~03:30 High during morning twilight at ~03:50 High in moonlight at ~04:00 1-
40o N High at ~03:50 High at ~04:00 High at ~04:10 High in moonlight at ~04:20 High in moonlight at ~04:20 1-
Equator High at ~04:40 High at ~04:40 High at ~04:40 High in moonlight at ~04:40 High in moonlight at ~04:30 1-
30o S Fairly high at ~04:50 Fairly high at ~04:40 High during morning twilight at ~04:40 High during morning twilight at ~04:30 High at ~04:10 1-

8P/Tuttle: A southern hemisphere morning comet visible in a 10-inch (25 cm) telescope
This comet begins the month in Hydra at magnitude 10.9. Look for a 1' coma. It should fade by about 1.0 magnitudes by month's end. The best visibility is mid-month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Low in the eastern sky during morning twilight at ~05:00 Low in the eastern sky during morning twilight at ~04:50 Low in the eastern sky during morning twilight at ~04:50 Low in the eastern sky during morning twilight at ~04:50 Not visible 1-
30o S Low in the eastern sky during morning twilight at ~05:00 Low in the eastern sky during morning twilight at ~04:50 Low in the eastern sky during morning twilight at ~04:40 Low in the eastern sky during morning twilight at ~04:30 Low in the eastern sky during morning twilight at ~04:20 1-

C/2017 K2 (PANSTARRS): An evening comet visible in a 10-inch (25 cm) telescope
This comet begins the month in Hercules at magnitude 13.0. Look for a 1.5' coma. It should brighten slowly.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N High at ~21:00 High at ~20:40 High during evening twilight at ~20:00 High during evening twilight at ~19:50 High at ~19:40 1-
40o N High at ~20:10 High at ~20:00 High during evening twilight at ~19:30 High at ~19:30 High at ~19:10 1-
Equator High at ~19:20 High in moonlight at ~19:10 High during evening twilight at ~19:00 High at ~19:10 High at ~19:00 1-
30o S Fairly high in the northern sky during evening twilight at ~19:00 Fairly high in the northern sky during evening twilight at ~19:10 Fairly high in the northern sky during evening twilight at ~19:10 Fairly high in the northern sky during evening twilight at ~19:10 Low in the northern sky during evening twilight at ~19:20 1-

C/2021 A1 (Leonard): A far-northern morning comet visible in a 12.5-inch (32 cm) telescope
This comet begins the month in Ursa Major at magnitude 14.5. Look for a 30" coma. It should brighten by about 1.3 magnitudes by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Low in the northern sky during morning twilight at ~03:20 Low in the eastern sky during morning twilight at ~03:40 Fairly high in the eastern sky during morning twilight at ~04:00 Fairly high in the eastern sky during morning twilight at ~04:10 1-
40o N Not visible Not visible Low in the eastern sky during morning twilight at ~04:20 Low in the eastern sky during morning twilight at ~04:30 Fairly high in the eastern sky during morning twilight at ~04:30 1-1, 6-
Equator Not visible Not visible Not visible Not visible Not visible  
30o S Not visible Not visible Not visible Not visible Not visible

19P/Borrelly: A southern hemisphere evening comet visible in a 12.5-inch (32 cm) telescope
This comet begins the month in Phoenix at magnitude 15.2. Look for a 30" coma. It should brighten by about 1.3 magnitudes, moving into Tucana by month's end. The best visibility is late in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Fairly high at ~01:10 Fairly high at ~00:40 Fairly high in the southern sky in moonlight at ~01:00 Fairly high in the southern sky at ~21:40 Fairly high at ~22:40 1-
30o S High at ~01:10 High at ~00:30 Fairly high during morning twilight at ~04:40 High at ~22:30 High at ~22:40 1-

C/2021 O1 (Nishimura): A solar conjunction comet visible in very large telescopes
This comet begins the month in Leo at magnitude 9.5. Look for a 0" coma. It should fade rapidly, moving into Virgo by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Not visible Not visible Not visible Not visible Not visible  
30o S Not visible Not visible Not visible Not visible Not visible

6P/d'Arrest: An evening comet visible in very large telescopes
This comet begins the month in Ophiuchus at magnitude 12.5. Look for a 3' coma. It should fade slowly, moving into Sagittarius by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Low in the southern sky during evening twilight at ~20:40 Not visible Not visible Not visible Not visible 1-8
40o N Fairly high in the southern sky at ~20:00 Fairly high in the southern sky in moonlight at ~19:50 Fairly high in the southern sky during evening twilight at ~19:30 Fairly high in the southern sky at ~19:20 Fairly high in the southern sky during evening twilight at ~19:00 1-
Equator High at ~19:20 High in moonlight at ~19:20 High during evening twilight at ~19:00 High at ~19:10 High at ~19:10 1-
30o S High at ~19:20 High in moonlight at ~19:20 Not visible High at ~19:30 High at ~19:30 1-15, 19-

7P/Pons-Winnecke: A southern hemisphere morning comet visible in very large telescopes
This comet begins the month in Phoenix at magnitude 12.5. Look for a 4.5' coma. It should fade by about 1.5 magnitudes, moving into Grus by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Fairly high at ~00:40 Fairly high at ~00:10 Not visible Fairly high at ~21:40 High at ~22:30 1-17, 22-
30o S High at ~00:40 High at ~00:10 Not visible High at ~22:20 High at ~22:30 1-17, 21-

252P/LINEAR: A southern hemisphere evening comet visible in very large telescopes
This comet begins the month in Virgo at magnitude 13.3. Look for a 55" coma. It should fade by about 1.1 magnitudes, moving into Libra by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator 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 Fairly high in the western sky during evening twilight at ~19:00 Fairly high in the western sky during evening twilight at ~19:00 1-
30o S Fairly high in the western sky 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 ~19:10 Fairly high in the western sky during evening twilight at ~19:20 Low in the western sky during evening twilight at ~19:20 1-

15P/Finlay: A morning comet visible in very large telescopes
This comet begins the month in Gemini at magnitude 13.3. Look for a 2' coma. It should fade by about 0.9 magnitudes, moving into Cancer by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Fairly high in the eastern sky during morning twilight at ~03:00 Fairly high at ~03:20 Fairly high at ~03:30 Not visible High in moonlight at ~04:00 1-19, 30-
40o N Fairly high at ~03:50 Fairly high at ~04:00 High at ~04:10 Not visible High in moonlight at ~04:20 1-19, 30-
Equator Fairly high at ~04:40 Fairly high at ~04:40 Fairly high at ~04:40 Not visible High in moonlight at ~04:30 1-18, 30-
30o S Low in the northern sky during morning twilight at ~05:00 Not visible Not visible Not visible Not visible 1-2, 4-9, 13-14

10P/Tempel: A morning comet visible in very large telescopes
This comet begins the month in Taurus at magnitude 13.7. Look for a 4' coma. It should fade by about 0.7 magnitudes, moving into Orion by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N High at ~03:50 High at ~04:00 Not visible Not visible Not visible 1-16
Equator High at ~04:40 High at ~04:30 Not visible Not visible Not visible 1-17
30o S High at ~04:40 High at ~04:30 Not visible Not visible Not visible 1-13

C/2020 J1 (SONEAR): An evening comet visible in very large telescopes
This comet begins the month in Virgo at magnitude 13.8. Look for a 1' coma. It should fade slowly.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Very low in the western sky during evening twilight at ~19:40 Not visible Not visible Not visible Not visible 1-1, 4-4
Equator 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 ~19:00 Not visible Not visible 1-19, 21-22
30o S Fairly high in the western sky during evening twilight at ~19:00 Low in the western sky during evening twilight at ~19:10 Low in the western sky during evening twilight at ~19:00 Not visible Not visible 1-19, 21-21

C/2019 T4 (ATLAS): A southern hemisphere morning comet visible in very large telescopes
This comet begins the month in Hydra at magnitude 14.4. Look for a 25" coma. It should brighten slowly. The best visibility is late in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Not visible Not visible Not visible Not visible Not visible  
30o S Not visible Not visible Low in the eastern sky during morning twilight at ~04:40 Low in the eastern sky during morning twilight at ~04:30 Low in the eastern sky during morning twilight at ~04:20 16-21, 24-

29P/Schwassmann-Wachmann: A morning comet visible in very large telescopes
This comet begins the month in Auriga at magnitude 14.4. Look for a 40" coma. It should brighten slowly.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N High at ~03:00 High at ~03:10 High at ~03:20 Fairly high in moonlight at ~23:50 High in moonlight at ~03:40 1-
40o N High at ~03:50 High at ~04:00 High at ~04:00 High in moonlight at ~00:40 High in moonlight at ~04:00 1-
Equator High at ~04:40 High at ~04:40 High at ~04:30 High during morning twilight at ~04:40 High at ~04:00 1-
30o S Fairly high in the northern sky at ~04:50 Fairly high in the northern sky at ~04:40 Fairly high in the northern sky during morning twilight at ~04:40 Fairly high in the northern sky during morning twilight at ~04:30 Fairly high in the northern sky at ~04:00 1-

C/2020 F5 (MASTER): A morning comet visible in very large telescopes
This comet begins the month in Pisces Austrinus at magnitude 14.8. Look for a 1' coma. It should fade slowly. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Low in the southern sky at ~00:00 Low in the southern sky at ~23:30 Not visible Low in the southern sky in moonlight at ~21:30 Fairly high in the southern sky at ~21:50 1-17, 20-
Equator High at ~00:00 High at ~23:30 Fairly high in moonlight at ~02:20 High at ~21:40 High at ~21:50 1-
30o S High at ~00:00 High at ~23:30 Low in the western sky during morning twilight at ~04:40 High at ~22:20 High at ~21:50 1-

246P/NEAT: An evening comet visible in very large telescopes
This comet begins the month in Sagittarius at magnitude 14.8. Look for a 30" coma. It should fade slowly. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Low in the southern sky during evening twilight at ~19:50 Low in the southern 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 ~19:10 Low in the southern sky during evening twilight at ~18:50 1-
Equator High at ~19:50 High in moonlight at ~19:50 High during evening twilight at ~19:00 High during evening twilight at ~19:00 High during evening twilight at ~19:00 1-
30o S High at ~19:50 High in moonlight at ~20:00 High during evening twilight at ~19:00 High at ~19:20 High during evening twilight at ~19:20 1-

C/2019 F1 (ATLAS-Africano): A southern hemisphere evening comet visible in very large telescopes
This comet begins the month in Octans at magnitude 14.8. Look for a 35" coma. It should fade slowly. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Not visible  
Equator Not visible Not visible Not visible Not visible Low in the southern sky at ~20:20  
30o S Fairly high at ~21:50 Fairly high in moonlight at ~21:30 Fairly high in the southern sky during morning twilight at ~04:40 Fairly high at ~20:40 High at ~20:20 1-

284P/McNaught: A morning comet visible in very large telescopes
This comet begins the month in Aquarius at magnitude 14.9. Look for a 40" coma. It should fade slowly.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N Fairly high in the southern sky at ~00:20 Fairly high in the southern sky at ~23:50 Not visible Low in the southern sky in moonlight at ~22:00 Low in the southern sky at ~22:20 1-17, 24-
40o N Fairly high at ~00:20 Fairly high at ~23:50 Not visible Fairly high in the southern sky at ~20:40 Fairly high at ~22:20 1-17, 22-
Equator High at ~00:20 High at ~23:50 Not visible High at ~21:30 High at ~22:20 1-17, 21-
30o S High at ~00:20 High at ~23:50 Not visible High at ~22:20 High at ~22:20 1-17, 21-

108P/Ciffreo: A morning comet visible in very large telescopes
This comet begins the month in Taurus at magnitude 15.2. Look for a 25" coma. It should brighten slowly, moving into Gemini by month's end.  FINDER CHART

Latitude Visibility September 4 Visibility September 11 Visibility September 18 Visibility September 25 Visibility October 2 Nights Visible
55o N High during morning twilight at ~03:00 High at ~03:20 High at ~03:30 High during morning twilight at ~03:50 High in moonlight at ~04:00 1-
40o N High at ~03:50 High at ~04:00 High at ~04:10 High in moonlight at ~04:20 High in moonlight at ~04:20 1-
Equator High at ~04:40 High at ~04:40 High at ~04:40 High during morning twilight at ~04:40 High in moonlight at ~04:30 1-
30o S Fairly high at ~04:50 Fairly high at ~04:40 Fairly high during morning twilight at ~04:40 Fairly high during morning twilight at ~04:30 Fairly high at ~04:10 1-

Summary Data for This Month's Telescopic Comets

Comets brighter than 16th 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/2021 O1 (Nishimura) Leo 9.5 1.2' 10.3 1.1' 11.2 1.0' 2021 July 26
C/2019 L3 (ATLAS) Auriga 10.0 2.1' 9.8 2.2' 9.7 2.3' 2021 August 31
C/2020 T2 (Palomar) Libra 10.5 4.0' 10.8 3.7' 11.1 3.4' 2021 August 30
8P/Tuttle* Hydra 10.9 1.0' 11.1 1.0' 11.8 1.0' 2021 August 18
4P/Faye Taurus 11.9 3.1' 11.8 3.4' 11.7 3.6' 2021 August 26
7P/Pons-Winnecke Phoenix 12.5 4.4' 13.2 3.8' 13.9 3.2' 2021 August 31
6P/d'Arrest Ophiuchus 12.5 2.9' 12.4 2.8' 12.7 2.6' 2021 August 31
67P/Churyumov-Gerasimenko Aries 12.8 58" 12.1 1.2' 11.5 1.4' 2021 August 21
C/2017 K2 (PANSTARRS) Hercules 13.0 1.3' 12.9 1.3' 12.8 1.3' 2021 August 31
252P/LINEAR Virgo 13.3 57" 13.8 54" 14.4 49" 2021 August 18
15P/Finlay Gemini 13.3 2.1' 13.8 2.0' 14.3 2.0' 2021 August 28
10P/Tempel Taurus 13.7 3.8' 14.0 3.9' 14.4 4.1' 2021 August 18
C/2020 J1 (SONEAR) Virgo 13.8 1.0' 14.0 60" 14.1 57" 2021 August 31
29P/Schwassmann-Wachmann Auriga 14.4 36" 14.3 38" 14.2 39" 2021 August 29
C/2019 T4 (ATLAS) Hydra 14.4 26" 14.4 26" 14.3 27" 2021 July 12
C/2021 A1 (Leonard) Ursa Major 14.5 24" 13.9 26" 13.1 30" 2021 August 31
246P/NEAT Sagittarius 14.8 29" 15.0 27" 15.2 25" 2021 August 10
C/2020 F5 (MASTER) Pisces Austrinus 14.8 1.1' 14.9 1.0' 15.0 1.0' 2021 August 31
C/2019 F1 (ATLAS-Africano) Octans 14.8 33" 14.9 32" 15.0 31" 2021 August 31
284P/McNaught Aquarius 14.9 38" 14.9 38" 15.0 36" 2021 August 12
C/2020 PV6 (PANSTARRS) Hercules 15.0 33" 15.2 30" 15.4 27" 2021 August 31
C/2018 U1 (Lemmon) Scorpius 15.1 26" 15.2 25" 15.3 24" 2021 August 31
106P/Schuster Taurus 15.1 35" 15.1 37" 15.1 39" 2021 July 16
P/1906 UA (Scheila) Leo 15.1 34" 15.1 34" 15.1 34" 2017 August 1
19P/Borrelly Phoenix 15.2 28" 14.5 29" 13.8 30" 2021 August 31
108P/Ciffreo Taurus 15.2 25" 15.0 27" 14.9 29" 2021 August 24
C/2021 A7 (NEOWISE) Leo 15.5 1.8' 15.6 1.8' 15.7 1.8' 2021 July 9
C/2019 N1 (ATLAS) Dorado 15.6 1.7' 15.8 1.6' 16.0 1.6' 2021 August 20
117P/Helin-Roman-Alu Virgo 15.8 1.0' 15.8 1.0' 15.8 59" 2021 August 11
C/2020 M5 (ATLAS) Canes Venatici 15.9 24" 16.0 23" 16.0 23" 2021 August 25
C/2021 E3 (ZTF) Lyra 16.0 24" 15.9 24" 15.7 24" 2021 August 25
22P/Kopff Virgo 16.6 40" 16.1 40" 15.7 41" 2021 June 30
132P/Helin-Roman-Alu Pisces 16.6 48" 16.2 54" 15.9 57" 2021 August 17
*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 visual observing custom charts for your location and telescope/binoculars: software for visual comet observing 

Select comets that are appropriate for your imaging system, and plan when they are best imaged: software for comet imaging 
 

Links

Skyhound's Guide to Comets
Skyhound's Guide to Finding Comets
BAA Comet Section
Weekly Information About Bright Comets
Cometography