Comet Chasing in December


Comet chasing is the visual observation of telescopic comets.

News


  • 174P/Echeclus had an outburst on December 8, brightening by several magnitudes. As of December 11, a small 20" coma has appeared, which is expected to grow in the coming days. Previous outbursts occurred in 2005 and 2011. Echeclus is a Centaur object that is capable of comet-like outbursts far from the sun. 

  • A/2017 U1 is the first interstellar object detected entering our solar system!  It was discovered on October 19 by the Pan-STARRS survey and put on the Potential Comets Confirmation Page of the Minor Planet Center to attract further observation, apparently assumed to be a comet based on its highly eccentric orbit alone. A provisional cometary designation of  C/2017 U1 (PANSTARRS) was assigned on October 25. But later observation revealed no cometary coma or tail, so the designation was changed to A/2017 U1. The object was detected already on the way out of our solar system, and was too faint to observe visually. It will continue to fade rapidly, and will never return. Nothing like this has been observed before. I have created a page with more details here, which will be updated as new research is published. 

  • 24P/Schaumasse passed perihelion in mid November. This comet was discovered in 1911 and has a 7.1 year orbital period. It has a long and interesting history, often "hit and miss," when it will be observed for several apparitions and then go missing for several more. Schaumasse was not observed in 2001 or 2009, but has roared back this year as bright a ever. Click here for a detailed history. 

  • C/2017 O1 (ASASSN) was 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. It passed perihelion in mid October, at which time the comet passed within 0.7 AU of the earth. 

  • C/2017 T1 (Heinze) will reach perihelion in late February 2018. It is brightening quickly and is currently predicted to reach maximum brightness of magnitude 10.5 in mid February.

  • 62P/Tsuchinshan was recovered in August. It had not been seen since 2004. It brightened significantly and passed perihelion in late November. It is now too close to the sun to be observed.

  • 29P/Schwassmann-Wachmann was very active in late August and September. It had the second of two outbursts that occurred within a few days of one another. This second outburst was the brightest since 2010, brightening it up to 12th magnitude. On July 2 in had an outburst that for the first time was caught as the outburst occurred (see https://www.britastro.org/node/10684). Primary 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 outbursts, such as the one ones recently, may occur 5-10 days afterward, each typically smaller than the last, but sometimes they can be even brighter than the first. 

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

  • 240P/NEAT had an outburst in August, apparently brightening by 3 magnitudes. It has since faded to 14th magnitude.

  • C/2015 ER61 (PANSTARRS) passed perihelion in early May and is on the way out and is only visible in large telescope. It had an outburst in early April, brightening by 1- 2 magnitudes. 

  • 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 19, 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.  

Read about the first interstellar object to pass through our solar system

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 December


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

62P/Tsuchinshan: A morning comet visible in small telescopes
This comet begins the month in Virgo at magnitude 9.8. Look for a 6' coma. It should fade slowly.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High during morning twilight at ~05:50 High during morning twilight at ~06:00 Fairly high at ~05:50 Fairly high at ~05:50 Fairly high at ~06:00 1-
40o N High during morning twilight at ~05:30 High during morning twilight at ~05:40 High at ~05:30 High at ~05:30 High at ~05:30 1-
Equator High during morning twilight at ~04:40 High during morning twilight at ~04:40 High at ~04:30 High at ~04:40 High at ~04:40 1-
30o S Fairly high in the eastern sky during morning twilight at ~03:40 Fairly high in the eastern sky during morning twilight at ~03:30 Fairly high in the eastern sky during morning twilight at ~03:20 Fairly high during morning twilight at ~03:20 Fairly high during morning twilight at ~03:30 1-

24P/Schaumasse: A morning comet visible in a 6-inch (15 cm) telescope
This comet begins the month in Virgo at magnitude 10.2. Look for a 4' coma. It should fade by about 1.4 magnitudes by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Fairly high during morning twilight at ~06:10 Fairly high in the southern sky during morning twilight at ~06:10 Fairly high in the southern sky at ~06:00 Fairly high in the southern sky at ~06:00 Fairly high in the southern sky at ~06:10 1-
40o N Fairly high during morning twilight at ~05:40 Fairly high during morning twilight at ~05:40 Fairly high at ~05:30 Fairly high at ~05:40 Fairly high at ~05:40 1-
Equator Fairly high during morning twilight at ~04:50 Fairly high during morning twilight at ~04:40 Fairly high at ~04:40 Fairly high at ~04:40 High at ~04:40 1-
30o S Low in the eastern sky during morning twilight at ~03:50 Low in the eastern sky during morning twilight at ~03:40 Low in the eastern sky during morning twilight at ~03:30 Low in the eastern sky during morning twilight at ~03:30 Fairly high in the eastern sky during morning twilight at ~03:30 1-

C/2017 O1 (ASASSN): A northern hemisphere morning comet visible in a 6-inch (15 cm) telescope
This comet begins the month in Cepheus at magnitude 10.2. Look for a 5' coma. It should fade by about 1.0 magnitudes by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High in moonlight at ~22:00 High at ~19:40 High at ~18:30 High at ~21:00 High at ~06:00 1-
40o N High in moonlight at ~21:50 High at ~19:30 High at ~18:40 High at ~21:30 Fairly high at ~05:10 1-
Equator Not visible Very low in the northern sky at ~19:20 Very low in the northern sky during evening twilight at ~19:10 Very low in the northern sky during evening twilight at ~19:10 Not visible 1-
30o S Not visible Not visible Not visible Not visible Not visible  

C/2016 R2 (PANSTARRS): An evening comet visible in a 6-inch (15 cm) telescope
This comet begins the month in Orion at magnitude 11.4. Look for a 2.5' coma. It should brighten slowly, moving into Taurus by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High in moonlight at ~00:10 High at ~23:00 High at ~23:00 High at ~22:30 Fairly high in moonlight at ~00:20 1-
40o N High in moonlight at ~00:10 High at ~23:20 High at ~23:00 High at ~22:20 High in moonlight at ~23:40 1-
Equator High in moonlight at ~00:10 High at ~23:40 High at ~23:00 High at ~22:20 High in moonlight at ~22:40 1-
30o S High in moonlight at ~00:20 High at ~23:40 High at ~23:00 High at ~22:40 High in moonlight at ~22:30 1-

C/2016 N6 (PANSTARRS): A northern hemisphere morning comet visible in an 8-inch (20 cm) telescope
This comet begins the month in Bootes at magnitude 13.3. Look for a 40" coma. It should brighten by about 0.5 magnitudes, moving into Draco by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High during morning twilight at ~06:10 Fairly high in the northern sky during evening twilight at ~17:50 High at ~06:00 High at ~06:00 High at ~06:00 1-
40o N Fairly high during morning twilight at ~05:40 High during morning twilight at ~05:40 High at ~05:40 High at ~05:40 High at ~05:40 1-
Equator Not visible Very low in the northern sky during morning twilight at ~05:00 Very low in the northern sky during morning twilight at ~04:50 Low in the northern sky during morning twilight at ~04:50 Low in the northern sky during morning twilight at ~04:50 1-1, 4-
30o S Not visible Not visible Not visible Not visible Not visible  

174P/Echeclus: An evening comet visible in an 8-inch (20 cm) telescope
On December 11, this Centaur/comet was in outburst in Aries at magnitude 13.0. Look for a 30" coma that may increase in size over time. FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High at ~21:00 High in moonlight at ~19:50 1-
40o N High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High at ~21:30 High in moonlight at ~19:50 1-
Equator High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High at ~22:10 High in moonlight at ~19:50 1-
30o S High in moonlight at ~21:50 High at ~21:20 High at ~21:00 High in moonlight at ~20:50 High during evening twilight at ~20:30 1-

29P/Schwassmann-Wachmann: An evening comet visible in a 10-inch (25 cm) telescope
This comet begins the month in Aquarius at magnitude 11.7. Look for a 2' coma. It should fade slowly, moving into Capricornus by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Fairly high in the southern sky during evening twilight at ~17:30 Low in the southern sky at ~17:50 Low in the southern sky during evening twilight at ~17:50 Low in the southern sky during evening twilight at ~17:40 Low in the southern sky during evening twilight at ~17:30 1-
40o N Fairly high during evening twilight at ~18:00 Fairly high in the southern sky at ~18:20 Fairly high in the southern sky at ~18:20 Fairly high in the western sky during evening twilight at ~18:10 Fairly high in the western sky during evening twilight at ~18:00 1-
Equator High during evening twilight at ~19:00 High at ~19:10 Fairly high at ~19:20 Fairly high during evening twilight at ~19:20 Fairly high in the western sky during evening twilight at ~19:10 1-
30o S Fairly high during evening twilight at ~20:00 Fairly high in the western sky during evening twilight at ~20:30 Fairly high in the western sky during evening twilight at ~20:30 Low in the western sky during evening twilight at ~20:30 Low in the western sky during evening twilight at ~20:10 1-

C/2015 O1 (PANSTARRS): A northern hemisphere morning comet visible in a 14-inch (36 cm) telescope
This comet begins the month in Hercules at magnitude 14.1. Look for a 20" coma. It should brighten slowly.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Fairly high in the eastern sky during morning twilight at ~06:20 Fairly high in the eastern sky during morning twilight at ~06:10 Fairly high in the eastern sky during morning twilight at ~06:10 Fairly high during morning twilight at ~06:10 Fairly high at ~06:10 1-
40o N Low in the eastern sky during morning twilight at ~05:50 Low in the eastern sky during morning twilight at ~05:50 Fairly high in the eastern sky during morning twilight at ~05:40 Fairly high in the eastern sky during morning twilight at ~05:40 Fairly high during morning twilight at ~05:50 1-
Equator Not visible Not visible Not visible Very low in the eastern sky during morning twilight at ~05:00 Low in the eastern sky during morning twilight at ~04:50 15-
30o S Not visible Not visible Not visible Not visible Not visible  

C/2017 T1 (Heinze): A morning comet visible in an 18-inch (46 cm) telescope
This comet begins the month in Hydra at magnitude 15.5. Look for a 25' coma. It should brighten rapidly, moving into Lynx by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Fairly high in moonlight at ~03:50 Fairly high in moonlight at ~03:50 High at ~03:10 High at ~02:20 High at ~06:00 1-
40o N High in moonlight at ~03:40 Low in the eastern sky at ~23:20 High at ~03:10 High at ~02:20 High at ~05:10 1-
Equator High in moonlight at ~03:20 Fairly high at ~23:50 High at ~03:10 High at ~02:20 Fairly high at ~04:00 1-
30o S High in moonlight at ~03:10 Fairly high at ~00:10 High at ~03:00 High at ~02:20 Low in the northern sky at ~03:20 1-

C/2015 V2 (Johnson): A southern hemisphere evening comet visible in very large telescopes
This comet begins the month in Pavo at magnitude 13.0. Look for a 60" coma. It should fade by about 0.7 magnitudes, moving into Indus by month's end. The best visibility is early in the month as seen from the southern hemisphere.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 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 southern sky during evening twilight at ~18:50 Low in the southern sky during evening twilight at ~19:10 Low in the southern sky during evening twilight at ~19:10 Low in the southern sky during evening twilight at ~19:10 Low in the southern sky during evening twilight at ~19:00 1-
30o S Fairly high during evening twilight at ~20:10 Fairly high in the southern sky at ~20:30 Fairly high in the southern sky at ~20:40 Fairly high in the southern sky during evening twilight at ~20:40 Fairly high in the southern sky during evening twilight at ~20:20 1-

C/2015 ER61 (PANSTARRS): An evening comet visible in very large telescopes
This comet begins the month in Aries at magnitude 13.9. Look for a 45" coma. It should fade by about 0.8 magnitudes by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N High in moonlight at ~22:10 High at ~21:30 High at ~21:00 High at ~21:00 High in moonlight at ~19:50 1-
40o N High in moonlight at ~22:10 High at ~21:30 High at ~21:00 High at ~21:30 High in moonlight at ~19:50 1-
Equator High in moonlight at ~22:00 High at ~21:30 High at ~21:00 High at ~22:10 High in moonlight at ~19:50 1-
30o S High in moonlight at ~22:00 High at ~21:30 High at ~21:00 High in moonlight at ~20:50 High during evening twilight at ~20:30 1-

C/2017 K6 (Jacques): An evening comet visible in very large telescopes
This comet begins the month in Hydrus at magnitude 14.3. Look for a 30" coma. It should remain constant, moving into Phoenix by month's end. The best visibility is late in the month as seen from the southern hemisphere.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Not visible Not visible Not visible Not visible Not visible  
40o N Not visible Not visible Not visible Not visible Very low in the southern sky in moonlight at ~19:10 28-
Equator Fairly high in the southern sky in moonlight at ~20:50 Fairly high at ~20:20 Fairly high at ~19:50 High in moonlight at ~19:30 High in moonlight at ~19:20 1-
30o S High in moonlight at ~21:10 High at ~20:50 High at ~20:50 High at ~22:40 High during evening twilight at ~20:30 1-

240P/NEAT: An evening comet visible in very large telescopes
This comet begins the month in Sculptor at magnitude 14.2. Look for a 1' coma. It should remain constant, moving into Cetus by month's end.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Very low in the southern sky in moonlight at ~19:10 Very low in the southern sky at ~18:50 Low in the southern sky at ~18:20 Low in the southern sky in moonlight at ~18:10 Low in the southern sky during evening twilight at ~17:50 1-
40o N Fairly high in the southern sky in moonlight at ~19:20 Fairly high in the southern sky at ~18:50 Fairly high in the southern sky at ~18:30 Fairly high in the southern sky in moonlight at ~18:20 Fairly high during evening twilight at ~18:10 1-
Equator High in moonlight at ~19:30 High at ~19:20 High at ~19:20 High in moonlight at ~19:20 High during evening twilight at ~19:10 1-
30o S High during evening twilight at ~20:20 High at ~20:40 High at ~20:40 High in moonlight at ~20:40 High during evening twilight at ~20:30 1-

C/2016 M1 (PANSTARRS): A far-northern evening comet visible in very large telescopes
This comet begins the month in Ophiuchus at magnitude 14.3. Look for a 50" coma. It should brighten slowly.  FINDER CHART
Latitude Visibility December 2 Visibility December 9 Visibility December 16 Visibility December 23 Visibility December 30 Nights Visible
55o N Fairly high in the western sky during evening twilight at ~17:20 Low in the western sky during evening twilight at ~17:40 Low in the western sky during evening twilight at ~17:40 Low in the eastern sky during morning twilight at ~06:20 Low in the eastern sky during morning twilight at ~06:20 1-
40o N Fairly high in the western sky during evening twilight at ~17:50 Low in the western sky during evening twilight at ~18:10 Low in the western sky during evening twilight at ~18:00 Very low in the eastern sky during morning twilight at ~06:00 Very low in the eastern sky during morning twilight at ~06:00 1-
Equator Not visible Not visible Not visible Not visible Not visible  
30o S Not visible Not visible Not visible Not visible Not visible  

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

December 1st

December 15th

December 31st

Observations as of (UT)
Mag Diam Mag Diam Mag Diam
62P/Tsuchinshan Virgo 9.8 6.1' 10.0 6.3' 10.3 6.5' 2017 November 26
C/2017 O1 (ASASSN) Cepheus 10.2 4.8' 10.6 4.3' 11.2 3.7' 2017 November 26
24P/Schaumasse Virgo 10.2 5.0' 10.7 5.0' 11.6 4.9' 2017 November 26
C/2016 R2 (PANSTARRS) Orion 11.4 2.6' 11.2 2.7' 11.1 2.7' 2017 November 26
174P/Echeclus Aries 15.0 5" 13.0 29" 13.1 28" 2017 December 11
C/2016 N6 (PANSTARRS) Bootes 13.3 34" 13.0 36" 12.8 39" 2017 November 16
29P/Schwassmann-Wachmann Aquarius 13.5 31" 13.6 30" 13.6 29" 2017 November 15
C/2015 ER61 (PANSTARRS) Aries 13.9 49" 14.2 44" 14.6 38" 2017 November 15
C/2015 O1 (PANSTARRS) Hercules 14.1 21" 14.1 22" 14.0 23" 2017 November 14
240P/NEAT Sculptor 14.2 1.1' 14.2 1.1' 14.3 1.0' 2017 November 8
C/2017 K6 (Jacques) Hydrus 14.3 32" 14.2 32" 14.2 32" 2017 November 10
C/2016 M1 (PANSTARRS) Ophiuchus 14.3 50" 14.2 51" 14.0 52" 2017 November 14
C/2016 N4 (MASTER) Draco 14.9 24" 15.0 23" 15.1 22" 2017 November 15
355P/LINEAR-NEAT Aries 15.0 41" 15.3 36" 15.7 31" 2017 November 23
C/2017 T1 (Heinze) Hydra 15.5 7" 13.9 12" 11.1 30" 2017 November 24

*In solar conjunction and generally not visible

For information about specific 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