Comet Chasing in August


Comet chasing is the visual observation of telescopic comets.

News


  • C/2017 O1 is a new discovery on July 19 by the All-Sky Automated Survey for Supernovae (ASASSN) program. This program is designed to discover supernovae. This is its first comet discovery. The preliminary orbit suggests that perihelion will be in mid October, at which time the comet will pass within 0.7 AU of the earth. Maximum brightness may be around magnitude 7 at that time.

  • C/2015 V2 (Johnson) passed perihelion in mid June and is visible in small telescopes.. 

  • C/2015 ER61 (PANSTARRS) will pass through the outskirts of Pleiades from August 16-20, which should make for some interesting chasing. This comet had an outburst in early April, brightening by 1- 2 magnitudes. It passed perihelion in early May and is on the way out, but remains bright enough to see in small telescopes. 

  • 29P/Schwassmann-Wachmann had another of its semi-regular outbursts on July 2, which for the first time was caught as the outburst occurred (see https://www.britastro.org/node/10684). The previous outburst was on June 27, when it brightened to magnitude 12.5. In fact, that was the second of two outbursts that occurred 5 days apart. Outbursts, resulting in a brightening of 0.5 - 1.0 magnitudes, occur roughly every 59 days, typically taking 5-10 days to subside. But up to three subsequent smaller outbursts, such as the one ones on July 2 and June 27, may occur 5-10 days afterward, each typically smaller than the last.

  • C/2017 K2 (PANSTARRS) is a new discovery from the PANSTARRS survey. This comet was discovered at an unusually large distance, over 16 AU from the sun! It is currently magnitude 18.8, which is bright for that distance. It won't pass perihelion until October of 2023, apparently at distance of 1.7 AU from the sun. This might possibly be a Great Comet... or not. We will just have to wait (and wait, and wait, and wait) and see.  

  • 41P/Tuttle-Giacobini-Kresak passed perihelion in mid April. In early April it passed within 0.1 AU of the earth. It is now fading.

  • C/2017 E4 (Lovejoy)  faded significantly on April 13, and appears to have disintegrated. There are no visual observations reported since it faded.  

  • 237P/LINEAR has not been observed visually since November when it was near perihelion. Afterward it was in conjunction with the Sun, but should have been picked up in morning twilight by the end of April. Based on how it appeared in November, it would be as bright as 11th magnitude. This comet was previously known as the asteroidal object 2002 LN13 but was recovered by WISE in 2010, appearing as a comet. It appears to have gone quiescent again, possibly as faint as 19th magnitude.  The next perihelion pass is in 2023. 

73P and fragment 73P-BT (lower right) on February 13. You can read an article about this image stack, and a movie made from the same set of images here

Comet Visibility in the Eyepiece

This page uses code developed for SkyTools 3 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 August


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

C/2017 O1 (O1): A morning comet visible in binoculars
This comet begins the month in Eridanus at magnitude 9.7. Look for a 6.5' coma. It should brighten by about 1.2 magnitudes, moving into Taurus by month's end.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Very low in the eastern sky during morning twilight at ~02:10 Low in the eastern sky during morning twilight at ~02:50 Fairly high in the eastern sky during morning twilight at ~02:40 Fairly high in the eastern sky during morning twilight at ~02:20 Fairly high during morning twilight at ~02:30 1-
40o N Fairly high in the eastern sky during morning twilight at ~03:10 Fairly high during morning twilight at ~03:40 High during morning twilight at ~03:50 High at ~03:30 High at ~03:40 1-
Equator High at ~04:40 High at ~04:50 High during morning twilight at ~05:00 High at ~04:40 High at ~04:40 1-
30o S High at ~05:10 High during morning twilight at ~05:40 High during morning twilight at ~05:20 High at ~05:00 High at ~04:50 1-

C/2015 V2 (Johnson): An evening comet visible in small telescopes
This comet begins the month in Centaurus at magnitude 9.5. Look for a 4.5' coma. It should fade by about 1.1 magnitudes, moving into Lupus by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Very low in the southern sky during evening twilight at ~20:40 Very low in the southern sky during evening twilight at ~20:10 Not visible Not visible Not visible 1-14
Equator High during evening twilight at ~19:20 High during evening twilight at ~19:10 High at ~19:20 Fairly high at ~19:20 Fairly high in moonlight at ~19:20 1-
30o S High in moonlight at ~18:50 High during evening twilight at ~18:50 High at ~19:00 High at ~19:10 High in moonlight at ~19:10 1-

C/2015 ER61 (PANSTARRS): A morning comet visible in a 10-inch (25 cm) telescope
This comet begins the month in Aries at magnitude 11.3. Look for a 4' coma. It should fade slowly, moving into Taurus by month's end. It will pass through the Pleiades late in the month. FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Fairly high in the eastern sky during morning twilight at ~01:10 Fairly high during morning twilight at ~02:10 Fairly high during morning twilight at ~02:20 Fairly high during morning twilight at ~02:10 High during morning twilight at ~02:30 1-
40o N Fairly high during morning twilight at ~03:10 High during morning twilight at ~03:40 High during morning twilight at ~03:40 High at ~03:30 High at ~03:40 1-
Equator High at ~04:50 High at ~04:50 High during morning twilight at ~05:00 High at ~04:40 High at ~04:40 1-
30o S Fairly high at ~05:20 Fairly high during morning twilight at ~05:40 Fairly high during morning twilight at ~05:20 Fairly high at ~05:00 Fairly high at ~04:50 1-

71P/Clark: An evening comet visible in a 12.5-inch (32 cm) telescope
This comet begins the month in Scorpius at magnitude 11.1. Look for a 8' coma. It should fade by about 0.9 magnitudes, moving into Corona Australis by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 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 ~20:50 Low in the southern sky during evening twilight at ~20:30 Low in the southern sky during evening twilight at ~20:40 Low in the southern sky during evening twilight at ~20:20 Low in the southern sky during evening twilight at ~20:10 1-
Equator Fairly high at ~23:20 High in moonlight at ~20:00 High at ~20:00 High at ~19:40 High in moonlight at ~19:30 1-
30o S High at ~23:40 High in moonlight at ~19:50 High at ~20:00 High at ~19:40 High at ~22:20 1-

217P/LINEAR: A morning comet visible in very large telescopes
This comet begins the month in Orion at magnitude 12.2. Look for a 5' coma. It should fade slowly.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Very low in the eastern sky during morning twilight at ~02:10 Low in the eastern sky during morning twilight at ~02:50 Low in the eastern sky during morning twilight at ~02:40 Low in the eastern sky during morning twilight at ~02:30 Low in the eastern sky during morning twilight at ~02:50 1-
40o N Fairly high in the eastern sky during morning twilight at ~03:20 Fairly high in the eastern sky during morning twilight at ~03:40 Fairly high in the eastern sky during morning twilight at ~03:50 Fairly high in the eastern sky during morning twilight at ~03:40 Fairly high during morning twilight at ~03:50 1-
Equator Fairly high at ~04:50 High at ~04:50 High during morning twilight at ~05:00 High at ~04:50 High at ~04:50 1-
30o S Fairly high at ~05:20 Fairly high during morning twilight at ~05:40 Fairly high during morning twilight at ~05:20 Fairly high at ~05:10 Fairly high at ~05:00 1-

29P/Schwassmann-Wachmann: An evening comet visible in very large telescopes
This comet begins the month in Capricornus at magnitude 13.2. It will likely fade back to 14-15th magnitude early in the month. Look for a 1.5' coma. It should remain constant, moving into Aquarius by month's end.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Fairly high in the southern sky during morning twilight at ~00:30 Fairly high in the southern sky during morning twilight at ~00:50 Low in the southern sky during evening twilight at ~21:40 Fairly high in the southern sky at ~23:30 Fairly high in the southern sky at ~23:00 1-
40o N Fairly high at ~01:00 Low in the western sky during morning twilight at ~03:40 Fairly high in the southern sky at ~21:50 Fairly high at ~23:30 Fairly high at ~23:00 1-
Equator High at ~01:00 Fairly high in the western sky at ~04:50 High at ~22:10 High at ~23:30 High at ~23:00 1-
30o S High at ~01:00 Low in the western sky during morning twilight at ~05:40 High at ~22:20 High at ~23:30 High at ~23:00 1-

C/2015 VL62 (Lemmon-Yeung-PANSTARRS): An evening comet visible in very large telescopes
This comet begins the month in Pegasus at magnitude 13.5. Look for a 4' coma. It should brighten slowly, moving into Aquarius by month's end. Note: due to the unusual combination of being faint and moving very quickly, this comet is difficult to make a monthly chart for. 
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N High during morning twilight at ~00:40 High during morning twilight at ~01:20 Fairly high during evening twilight at ~21:40 High at ~23:40 Fairly high at ~22:50 1-
40o N High at ~02:20 High during morning twilight at ~03:40 High at ~21:50 High at ~23:40 High at ~22:50 1-
Equator High at ~02:20 Fairly high at ~04:50 High at ~22:10 High at ~23:40 High at ~22:50 1-
30o S High at ~02:20 Low in the western sky during morning twilight at ~05:40 Fairly high at ~22:20 High at ~23:40 High at ~22:50 1-

213P/Van Ness: An evening comet visible in very large telescopes
This comet begins the month in Sagittarius at magnitude 13.4. Look for a 6' coma. It should fade slowly. The best visibility is mid-month as seen from the southern hemisphere.  FINDER CHART
Latitude Visibility July 29 Visibility August 5 Visibility August 12 Visibility August 19 Visibility August 26 Nights Visible
55o N Very low in the southern sky during evening twilight at ~22:50 Not visible Very low in the southern sky during evening twilight at ~21:40 Very low in the southern sky during evening twilight at ~21:40 Very low in the southern sky during evening twilight at ~21:10 11-
40o N Fairly high in the southern sky at ~23:00 Fairly high in the southern sky in moonlight at ~21:40 Fairly high in the southern sky at ~21:20 Fairly high in the southern sky at ~21:00 Fairly high in the southern sky at ~21:30 1-
Equator High at ~23:20 High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High at ~22:00 1-
30o S High at ~23:40 High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High at ~22:20 1-

Summary Data for This Month's Telescopic Comets


Comets 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

August 1st

August 15th

August 31st

Observations as of (UT)
Mag Diam Mag Diam Mag Diam
C/2015 V2 (Johnson) Centaurus 9.5 5.6' 10.0 4.8' 10.5 4.1' 2017 July 25
C/2017 O1 (O1) Eridanus 9.7 10.2' 9.1 11.9' 8.4 14.4' 2017 July 26
71P/Clark Scorpius 11.1 3.0' 11.5 2.7' 12.0 2.3' 2017 July 25
C/2015 ER61 (PANSTARRS) Aries 11.3 3.0' 11.5 3.0' 11.7 3.0' 2017 July 26
217P/LINEAR Orion 12.2 1.4' 12.4 1.4' 12.7 1.4' 2017 July 26
41P/Tuttle-Giacobini-Kresak Serpens Cauda 12.8 3.8' 14.4 3.0' 16.2 2.4' 2017 July 15
29P/Schwassmann-Wachmann Capricornus 13.2 1.2' 13.2 1.2' 13.2 1.2' 2017 July 26
213P/Van Ness Sagittarius 13.4 26" 13.5 25" 13.7 23" 2017 July 1
C/2015 VL62 (Lemmon-Yeung-PANSTARRS) Pegasus 13.5 59" 13.3 1.1' 13.3 1.0' 2017 July 26
65P/Gunn Libra 14.3 53" 14.5 50" 14.6 46" 2017 July 1
C/2016 R2 (PANSTARRS) Eridanus 14.4 1.1' 14.1 1.2' 13.8 1.3' 2017 July 5
C/2015 O1 (PANSTARRS) Hercules 14.5 16" 14.5 15" 14.6 14" 2017 July 15
C/2016 N4 (MASTER) Cassiopeia 14.7 7" 14.6 7" 14.5 7" 2017 July 7
C/2016 M1 (PANSTARRS) Hercules 15.0 6" 14.9 6" 14.8 6" 2017 July 8

*In solar conjunction and generally not visible

For the latest news and comet observations see the ICQ/CBAT/MPC: Recent Comet Magnitude Estimates page.  The Astronomical Headlines page of the IAU is also a good source of information, particularly for recent discoveries.

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

Join the Comet Chasing discussion group 

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

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

Links

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