Comet Section        

 
 

December 3, 2019 – ALPO Comet News for December 2019

C/2017 T2 (PANSTARRS) is well placed in the evening sky for northern observers and should become brighter than 10th magnitude this month. CCD imagers are encouraged to image a number of fainter comets this month. In particular, the following are of interest. Interstellar visitor 2I/Borisov will be at its best around 15th magnitude. December and January will see short-period comet 289P/Blanpain pass within 0.09 au of the Earth. How bright this comet gets is uncertain as it is a faint, outburst prone object. Speaking of outburst prone comets, the British Astronomical Society invites CCD photometrists to join their effort to monitor the outbursts of 29P/Schwassmann-Wachmann.

The monthly ALPO Comet News PDF can be found here. An edited version of this report is posted on the Cloudy Nights forum at (https://www.cloudynights.com/topic/685850-alpo-comet-news-for-december-2019/). Everyone is invited to join the discussion at our Cloudy Nights forum.

- Carl Hergenrother

 
 

November 2, 2019 – ALPO Comet News for November 2019

November finds us in-between bright comets. C/2018 W2 (Africano) is now too faint for small aperture telescopes while C/2017 T2 (PANSTARRS) is at least a month away from becoming an easy object. Fortunately it will continue to brighten over the next few months and should provide a nice target for much of the first half of 2020. CCD imagers are encouraged to keep a detector on interstellar comet 2I/Borisov which will be around 15-16th magnitude this month.

Other comets brighter than 13th magnitude this month include 29P/Schwassmann-Wachmann, 260P/McNaught, and C/2018 N2 (ASASSN). Fainter comets of interest include 289P/Blanpain and the aforementioned 2I/Borisov.

The monthly ALPO Comet News PDF can be found here. An edited version of this report is posted on the Cloudy Nights forum at (https://www.cloudynights.com/topic/682477-alpo-comet-news-for-november-2019/). Everyone is invited to join the discussion at our Cloudy Nights forum.

 
 

October 4, 2019 – ALPO Comet News for October 2019

I’m mixing things up a bit this month. The monthly ALPO Comet News are now be distributed as PDFs (link to this month’s PDF). A shorter version of this report is also posted on the Cloudy Nights forum. If you’d like to join in the discussion, I encourage you to visit our Cloudy Nights forum.

C/2018 W2 (Africano) starts the month around magnitude 8.5 though it will rapidly fade as the month progresses. C/2017 T2 (PANSTARRS) will still be 11th magnitude at the end of September but should replace Africano as the brightest observable comet. CCD observers can look forward to observing the first confirmed interstellar comet, 2I/2019 Q4 (Borisov). Other comets observable this month at brighter than 12th magnitude include 68P/Klemola, 260P/McNaught, and C/2018 N2 (ASASSN).

 
 

NEW BRIGHT COMET – C/2018 V1 (MACHHOLZ-FUJIKAWA-IWAMOTO)

2018-November-11

Wow, this is cool in so many ways!
Nowadays even comets that become bright are discovered months to years before perihelion and usually by professional surveys. The latest comet to be discovered is sort of a throwback to the old days of comet hunting. For starters, the comet was relatively bright at discovery (10th magnitude, though recent observations suggest it may have brightened to 7th or 8th magnitude). Also it was found by three independent amateurs and now shares all three of their names. And lastly, one of the discoverers is our very own former Comet Section Coordinator, Don Machholz, who found the comet visually!

C/2018 V1 (Machholz-Fujikawa-Iwamoto) has been officially announced on CBET 4569 and MPEC 2018-V151. The comet was found by all three discoverers within about 8 hours of each other. Don visually used a 0.47-m reflector at 113x while Fujikawa used a CCD + 120-mm-f.l. f/3.5 lens and Iwamoto used a 10-cm f/4.0 Pentax SDUF II telephoto lens and a Canon EOS 6D camera.

The comet may be experiencing an outburst. Hence, why it was suddenly discovered as a bright object by three observers within ~8 hours of each other. It brightness behavior is definitely suggestive of an outburst. It was reported by Machholz at magnitude 10.5 at discovery. J. J. Gonzalez saw the comet at magnitude 9.9 on Nov. 9.22 UT while Chris Wyatt saw it even brighter at 8.9 on Nov. 10.72 UT. Charles Morris just posted an estimate on comets-ml from last night (Nov. 11.55 UT) placing the comet closer to magnitude 7.5!

This is Don’s 12th discovery and first since C/2010 F4 after 746 hours of visual searching. His other discoveries include 96P/Machholz, 141P/Machholz, C/1978 R3 (Machholz), C/1985 K1 (Machholz), C/1988 P1 (Machholz), C/1992 F1 (Tanaka-Machholz), C/1992 N1 (Machholz), C/1994 N1 (Nakamura-Nishimura-Machholz), C/1994 T1 (Machholz) and C/2004 Q2 (Machholz). The comet is the seventh to bear Shigehisa Fujikawa’s name. He also independently discovered two comets in 1968, C/1968 N1 (Honda) and C/1968 H1 (Tago-Honda-Yamamoto). His other discoveries include C/1969 P1 (Fujikawa), C/1970 B1 (Daido-Fujikawa), C/1975 T1 (Mori-Sato-Fujikawa), C/1983 J1 (Sugano-Saigusa-Fujikawa), C/2002 X5 (Kudo-Fujikawa) and a rediscovery of comet 72P/Denning-Fujikawa. This is Masayuki Iwamoto’s second comet after C/2013 E2 (Iwamoto).

The comet marks the first visual comet discovery in almost exactly 8 years since the discovery of 332P/2010 V1 (Ikeya-Murakami). It is also the first comet to bear three names since C/2015 VL62 (Lemmon-Yeung-PanSTARRS) and the first to bear three amateur names in 24 years! Don was involved with that comet as well [C/1994 N1 (Nakamura-Nishimura-Machholz)].

The MPEC 2018-V151 orbit makes C/2018 V1 a long-period comet with perihelion on December 3 at 0.39 AU and inclination of 144 degrees. The comet was too close to the Sun to be seen until a few weeks ago. Unfortunately, it will drop back into the glare of the Sun in another week or two. After that the comet will not be visible to northern hemisphere observers. Southern hemisphere observers should be able to image the comet again starting next February. I say imaging since the comet will then be much further from the Sun and Earth at that time. Currently the comet is a morning object in Virgo, C/2018 V1 can be seen a degree to the east of the well known variable star Porrima (gamma Vir).

Congratulations to Don, Fujikawa-san and Iwamoto-san!

Below, a 60-second image of C/2018 V1 (Machholz-Fujikawa-Iwamoto) was taken by Martin Mobberley via iTelescope’s T14 FSQ106 telescope in New Mexico.

 
 

ALPO COMET NEWS FOR NOVEMBER 2018

2018-November-5

Comet 46P/Wirtanen rapidly brightens this month as it approaches to within 0.078 AU of the Earth on Dec 16. Depending on how dark your skies are, Wirtanen may be a naked eye object in December (or even as early as late November). Wirtanen isn’t the only cometary attraction this month. Two short-period comets come to perihelion in November. Both 38P/Stephan-Oterma and 64P/Swift-Gehrels should peak between magnitude 9 and 9.5 this month.

Bright Comets (magnitude < 10)

38P/Stephan-Oterma – Halley family comet 38P/Stephan-Oterma has an orbital period of ~38 years and is returning for the first time since 1980. This comet has a bit of an interesting backstory. In 1867, it was first sighted by Jérôme E. Coggia (Marseilles, France) who thought he had found an uncatalogued nebula. Over the following nights, followup observations by E. J. M. Stephan (Marseilles, France) uncovered the true nature of the object. For some reason, the discovery announcement cited Stephan as the discoverer with no mention of Coggia. After being missed at its next return in 1904, the comet was photographically rediscovered in 1942 by Liisi Oterma (Turku, Finland).

Stephen-Oterma is a morning object though it should be high enough to observe for most northern observers by 11 pm to midnight. This month should see the comet at its brightest (between magnitude 9.0 and 9.5) as it reaches perihelion (1.59 AU) on November 10 and closest approach to Earth (0.77 AU) on December 17. It will be moving through Gemini (Nov 1-25, 28-29) and Cancer (25-28, 29-30).

38P/Stephan-Oterma
T = 2018-Nov-10  q = 1.59 AU   Short-Period comet  Period = 38.0 yr
     Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01   9.6   07 10  +18 37   1.593   0.935   111    Gem
2018-11-11   9.4   07 32  +21 30   1.588   0.872   116    Gem
2018-11-21   9.3   07 52  +24 50   1.593   0.823   122    Gem
2018-12-01   9.3   08 09  +28 34   1.608   0.788   129    Cnc

46P/Wirtanen – The brightest comet of the year will be 46P/Wirtanen which passes within 0.078 AU of the Earth in mid-December.
While the comet is still a southern object, this month sees the comet start its acceleration northward across the sky. Starting the month at a declination of -33 degrees, Wirtanen ends the month at -19 degrees as it moves through Fornax (Nov 1-27) and Cetus (27-30). Next month the comet will be located at significantly more northern declinations.

Chris Wyatt reported Wirtanen to be at magnitude 7.7 on November 3. This is very close to the prediction based on past apparitions. Its rapid brightening should bring the comet to magnitude 7.0 by the 10th, 6.0 by the 20th and 5.0 by the 28th. Recent CCD images by Martin Mobberley have even caught the development of a gas tail.

Assuming it behaves as in the past, Wirtanen should peak around magnitude 3 in mid-December. Note, that as a short-period comet, Wirtanen is likely to be a large diffuse object around the time of closest approach. It is possible its coma diameter will be in excess of 1 degree. Already visual observations by Chris Wyatt and CCD observations by Raymond Ramlow show Wirtanen to possess a coma with a diameter of 20+ arc minutes (0.33 degrees). Even at its brightest, do not expect the comet to appear as bright as a 3rd magnitude star since its light will be spread over a large area. Observers may need a relatively dark sky to see Wirtanen with the naked eye.

46P/Wirtanen
T = 2018-Dec-12  q = 1.06 AU   Short-Period comet  Period = 5.4 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01   8.0   01 59  -33 03   1.195   0.275   132    For
2018-11-11   6.9   02 02  -32 33   1.140   0.221   128    For
2018-11-21   5.8   02 11  -29 05   1.096   0.169   126    For
2018-12-01   4.6   02 32  -19 51   1.068   0.121   129    Cet

64P/Swift-Gehrels – Comet Swift-Gehrels was originally discovered visually by Lewis Swift (Rochester, New York) in 1889. Swift was also the discoverer of the Perseid parent body, Swift-Tuttle. After the 1889 apparition Swift’s comet went unobserverd until 1973 when its was rediscovered by Tom Gehrels on photographic plates taken at Palomar Observatory in southern California. 2018 marks Swift-Gehrels’ 7th observed return. Since its discovery in 1889, the comet’s orbit has been fairly stable with an orbital period of 9.4 years and perihelion distance near its current value of 1.39 AU. Not an especially bright object, this year’s return will be its best known return with a minimum Earth-comet distance of 0.44 AU on October 28. You will have to wait till 2092 for another return as good as this year’s though the 2046 return will be just a little worse than this year.

64P has already shown some excitement with a short lived outburst that saw it brighten by ~2-3 magnitudes to around 13th magnitude in mid-August. After its outburst, Swift-Gehrels seemed to be running a little brighter than expected. The most recent magnitude estimates from Chris Wyatt and Salvador Aguirre place the comet around magnitude 9.9-10.0 which is fairly close to its predicted brightness.

Now an evening object, Swift-Gehrels can be seen moving through Andromeda (Nov 1-25) and Triangulum (25-30). Perihelion occurs on November 3 at 1.39 AU and closest approach to Earth was a week earlier on October 27 at 0.44 AU. In the past, the comet reached its peak intrinsic brightness five weeks after perihelion. If it follows the same pattern, Swift-Gehrels should continue to brighten to a late November peak at magnitude 9.5.

64P/Swift-Gehrels
T = 2018-Nov-03  q = 1.39 AU   Short-Period comet  Period = 8.9 yr.
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  10.1   00 48  +36 53   1.394   0.446   148    And
2018-11-11   9.7   01 02  +36 45   1.396   0.457   146    Tri
2018-11-21   9.5   01 20  +35 54   1.408   0.481   144    Tri
2018-12-01   9.5   01 42  +34 34   1.431   0.519   141    Tri

Faint Comets (between magnitude 10 and 13)

21P/Giacobini-ZInner - Short-period comet 21P/Giacobini-Zinner is now two months past its September perihelion. After reaching a peak brightness of around magnitude 7.0, the comet faded more rapidly than expected in October. A CCD observation by Raymond Ramlow on November 4 found Giacobini-Zinner at magnitude 10.4.

November should see the comet steadily fade as it moves away from the Sun and Earth. The comet also continues moving deeper into the southern sky. Visual and CCD observers can continue to enjoy the comet moving against the rich Milky Way constellations of Canis Major (Nov 1-11) and Puppis (11-30).

Looking ahead, Giacobini-Zinner’s next return in 2025 will be very poor with the comet located on the other side of the Sun at perihelion. In 2031 the comet will be better placed with a minimum Earth-comet distance of 0.55 AU (versus 0.39 AU this year) and a slightly larger perihelion distance of 1.07 AU (versus 1.01 AU this year). The comet should brighten to magnitude 8 or so that year.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  10.4   07 25  -28 08   1.245   0.660    95    CMa
2018-11-11  11.2   07 24  -33 09   1.326   0.727    99    CMa
2018-11-21  11.9   07 17  -36 42   1.412   0.793   104    Pup
2018-12-01  12.5   07 07  -38 53   1.501   0.859   108    Pup

C/2016 M1 (PANSTARRS) – Comet C/2006 M1 (PANSTARRS) continues to slowly fade. Visual observations by Chris Wyatt on November 3 found the comet at magnitude 10.4. Having passed perihelion on August 10 at 2.21 AU and now moving away from both the Earth and Sun, C/2016 M1 should continue to slowly fade as it moves through the southern constellations of Circinus and Apus.

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  10.7   14 50  -68 16   2.406   2.848    54    Cir
2018-11-11  10.9   15 03  -70 56   2.453   2.906    53    Aps
2018-11-21  11.0   15 20  -73 52   2.504   2.950    54    Aps
2018-12-01  11.2   15 42  -77 04   2.558   2.982    55    Aps

C/2016 N6 (PANSTARRS) – Yet another faint, high q, PANSTARRS discovery, C/2016 N6 was imaged by Raymond Ramlow at magnitude 12.6 on November 2nd and observed visually by J. J. Gonzalez at magnitude 11.8 on October 20. The comet is now 4 months past perihelion (2.67 AU on July 18, 2018). A decreasing Earth-comet distance will result in the comet staying near magnitude 12 even though it is moving away from the Sun in November.

C/2016 N6 (PANSTARRS)
T = 2018-Jul-18 q = 2.67 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  12.2   08 54  +02 17   2.889   2.836    83    Hya
2018-11-11  12.2   08 47  -01 09   2.930   2.699    93    Hya
2018-11-21  12.2   08 37  -04 44   2.974   2.575   104    Hya
2018-12-01  12.2   08 23  -08 28   3.020   2.473   114    Hya

Other Comets of Interest

(944) Hidalgo and (3552) Don Quixote – Two bright low activity or dormant comets come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though a tail was seen in 2009 with the Spitzer IR space telescope and again this March at visible wavelengths with a 4.1-m telescope. This month Don Quixote is fading from magnitude 16.5 to 17.2. (944) Hidalgo reaches peak brightness at magnitude 14.3 this month. Unlike Don Quixote, Hidalgo has shown no cometary activity so far.

(944) Hidalgo
T = 2018-Oct-26  q = 1.95 AU   Extinct comet       Period = 13.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  14.4   08 35  +70 59   1.948   1.476   102    UMa
2018-11-11  14.3   09 34  +73 38   1.954   1.456   104    Dra
2018-11-21  14.3   10 37  +75 27   1.964   1.448   105    Dra
2018-12-01  14.3   11 36  +76 34   1.979   1.450   107    Dra
(3552) Don Quixote
T = 2018-May-07  q = 1.24 AU   Extinct comet       Period =  8.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-11-01  16.5   01 29  +54 13   2.393   1.556   138    Cas
2018-11-11  16.7   01 12  +53 05   2.475   1.647   138    Cas
2018-11-21  16.9   01 01  +51 31   2.557   1.759   135    Cas
2018-12-01  17.2   00 56  +49 49   2.638   1.891   130    Cas

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)

 
 

ALPO COMET NEWS FOR OCTOBER 2018

2018-OCTOBER-5

This month will up to four comets as bright or brighter than 10th magnitude. 21P/Giacobini-Zinner will fade from 7th to 9th magnitude as it rapidly moves south. As 21P fades, the next bright comet, 46P/Wirtanen, quickly brightens to take its place. In addition to 46P, comets 38P/Stephan-Oterma and 64P/Swift-Gehrels brighten to near or slightly brighter than magnitude 10.0.

Bright Comets (magnitude < 10)

21P/Giacobini-Zinner – Short-period comet 21P/Giacobini-Zinner starts the month as the brightest comet at magnitude ~7.7. Now a few weeks past perihelion and its closest approach to Earth, 21P will be fading this month and should hand its ‘brightest comet’ title to 46P/Wirtanen towards the end of the month.

G-Z has provided observers with a number of memorable views as it traveled through the star, cluster and nebula-rich winter Milky Way. October will be no different as it moves southwards through Monoceros (Oct 1-9) and Canis Major (9-31). Close approaches to the following deep sky objects occur this month: open clusters NGC 2311 (Oct 3), M50 (Oct 6/7), NGC 2335 (Oct 8), Cr 465 (Oct 8/9), NGC 2343 (Oct 8/9), NGC 2345 (Oct 11), NGC 2360 (Oct 14). CCD images have shown a nice long dust tail. Observers are encouraged to watch the evolution of 21P’s dust tail as we pass through orbit plane crossing on October 9th.

Visual observations submitted to the ALPO over the last week or so show 21P to be between magnitude 7.4 and 7.6. This suggests the comet is running a little fainter than expected. Then again the Moon had been bright and/or nearby and possibly hid the outer extent of 21P’s coma resulting in fainter estimates.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01   7.6   06 51  +00 03   1.055   0.453    84    Mon
2018-10-11   8.2   07 08  -11 42   1.103   0.515    87    CMa
2018-10-21   8.8   07 19  -20 41   1.165   0.583    91    CMa
2018-10-31   9.5   07 24  -27 33   1.237   0.653    95    CMa

38P/Stephan-Oterma – Comet Stephan-Oterma has an orbital period of ~38 years and is returning for the first time since 1980. This comet has a bit of an interesting backstory. In 1867, it was first sighted by Jérôme E. Coggia (Marseilles, France) who thought he had found an uncatalogued nebula. Over the following nights, followup observations by E. J. M. Stephan (Marseilles, France) uncovered the true nature of the object. For some reason, the discovery announcement cited Stephan as the discoverer with no mention of Coggia. After being missed at its next return in 1904, the comet was photographically rediscovered in 1942 by Liisi Oterma (Turku, Finland).

This month, 38P will be a morning object in Orion and Gemini as it brightens from 11th to just brighter than 10th magnitude. Ultimately the comet will peak around magnitude 9.0 to 9.5 in late November after its perihelion on November 10 at 1.59 AU. In 1980, Stephan-Oterma approached to within 0.59 AU of Earth and brightened to between magnitude 8.5 and 9.0. This year’s return will be a little further away at 0.76 AU, hence the slightly fainter maximum brightness.

38P/Stephan-Oterma
T = 2018-Nov-10  q = 1.59 AU   Short-Period comet  Period = 38.0 yr
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  10.8   05 55  +11 56   1.670   1.199    98    Ori
2018-10-11  10.4   06 20  +13 47   1.636   1.102   102    Ori
2018-10-21  10.0   06 44  +15 54   1.610   1.016   106    Gem
2018-10-31   9.7   07 08  +18 21   1.594   0.941   111    Gem

46P/Wirtanen – The brightest comet of the year should be 46P/Wirtanen which will pass within 0.08 AU of the Earth in mid-December. Wirtanen will be located around a southern declination of -30 degrees till late November (in the constellations of Cetus and Fornax). The comet will rapidly brighten from 11th to 8th magnitude this month. The comet will become better placed for northern observers starting in late November as it rapidly moves north. Assuming it behaves as it has in the past, Wirtanen should peak around magnitude 3 in mid-December. Note, that as a short-period comet, Wirtanen is likely to be a large diffuse object around the time of closest approach. It is possible its coma diameter will be in excess of 1 degree. Do not expect it to appear as bright as a 3rd magnitude star since it light will be spread over a large area. Observers may need a relatively dark sky to see Wirtanen with the naked eye.

46P/Wirtanen
T = 2018-Dec-12  q = 1.06 AU   Short-Period comet  Period = 5.4 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  11.3   01 53  -26 14   1.418   0.479   144    For
2018-10-11  10.3   01 56  -29 09   1.340   0.404   141    For
2018-10-21   9.2   01 57  -31 35   1.267   0.339   137    For
2018-10-31   8.1   01 59  -32 59   1.201   0.280   132    For

Faint Comets (between magnitude 10 and 13)

64P/Swift-Gehrels – Comet Swift-Gehrels was originally discovered visually by Lewis Swift (Rochester, New York) in 1889. Swift was also the discoverer of the Perseid parent body, Swift-Tuttle. After the 1889 apparition Swift’s comet went unobserverd until 1973 when its was rediscovered by Tom Gehrels on photographic plates taken at Palomar Observatory in southern California. 2018 marks Swift-Gehrels’ 7th observed return. Since its discovery in 1889, the comet’s orbit has been fairly stable with an orbital period of 9.4 years and perihelion distance near its current value of 1.39 AU. Not an especially bright object, this year’s return will be its best known return with a minimum Earth-comet distance of 0.44 AU on October 28. You will have to wait till 2092 for another return as good as this year’s though the 2046 return will just a little worse.

64P has already shown some excitement with a short lived outburst that saw it brighten by ~2-3 magnitudes to around 13th magnitude in mid-August. Swift-Gehrels has since settled down again and, unless it outbursts again, should brighten from 15th to 12th magnitude this month. Peak brightness will be around magnitude 9.5 in late November.

The magnitudes given below are based on 64P’s behavior during its 1981 apparition. Even considering its mid-August outburst, 64P seems to be running brighter than predicted. Observations submitted to COBS over the past few days show the comet to be between magnitude 10.1 and 11.4.

64P/Swift-Gehrels
T = 2018-Nov-03  q = 1.39 AU   Short-Period comet  Period = 8.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  12.2   00 28  +31 27   1.452   0.491   151    And
2018-10-11  11.4   00 32  +34 10   1.423   0.463   151    And
2018-10-21  10.7   00 37  +35 59   1.403   0.448   150    And
2018-10-31  10.1   00 46  +36 51   1.394   0.445   149    And

C/2016 M1 (PANSTARRS) – Visual observations by Chris Wyatt on October 1 found the comet at magnitude 10.2. Having passed perihelion on August 10 at 2.21 AU and now moving away from both the Earth and Sun, C/2016 M1 should continue to slowly fade as it moves through the southern constellations of Centaurus and Circinus.

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet - dynamically old
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  10.1   14 27  -61 51   2.290   2.564    62    Cen
2018-10-11  10.3   14 32  -63 37   2.322   2.673    58    Cen
2018-10-21  10.5   14 39  -65 40   2.360   2.766    56    Cir
2018-10-31  10.7   14 49  -68 01   2.402   2.842    54    Cir

C/2016 R2 (PANSTARRS) - CO+ rich comet C/2016 R2 (PANSTARRS) continues its very slow fade. Thanks to its large perihelion distance (2.60 AU), the comet experiences slow changes in its heliocentric and geocentric distances. The comet should remain around 12th magnitude this month as it pulls away from the Sun in the northern morning sky.

C/2016 R2 (PANSTARRS)
T = 2018-May-02  q = 2.60 AU   Long-Period comet - dynamically old
 Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  11.7   10 58  +50 43   2.869   3.532    42M   UMa
2018-09-11  11.8   11 27  +49 40   2.914   3.538    44M   UMa
2018-09-21  11.9   11 56  +48 29   2.962   3.544    47M   UMa
2018-10-01  12.0   12 23  +47 14   3.012   3.552    50M   CVn

Other Comets of Interest

(944) Hidalgo and (3552) Don Quixote – Two bright low activity or dormant comets come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though a tail was seen in 2009 with the Spitzer IR space telescope and again this March at visible wavelengths with a 4.1-m telescope. This month Don Quixote is near magnitude 16.3. (944) Hidalgo is still inbound and will peak in brightness at 14.3 in November. Unlike Don Quixote, Hidalgo has shown no cometary activity so far.

364P/PANSTARRS – 364P/PANSTARRS is a low activity comet that only shows activity at small heliocentric distances. Discovered in 2013, 364P is making its second observed return with perihelion having occurred in late June at 0.80 AU. Cometary activity has now ceased though a residual dust tail is still visible. This month CCD observers will be able to image the bare nucleus of 364P as it fades from magnitude 17.7 to 19.3.

364P/PANSTARRS
T = 2018-Jun-24  q = 0.80 AU   Short-Period comet  Period =  4.9 yr
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  17.6   00 02  -23 18   1.625   0.668   153    Cet
2018-10-11  18.1   23 49  -20 18   1.728   0.801   147    Aqr
2018-10-21  18.7   23 42  -17 32   1.828   0.953   139    Aqr
2018-10-31  19.3   23 40  -15 01   1.927   1.122   131    Aqr
(944) Hidalgo
T = 2018-Oct-26  q = 1.95 AU   Extinct comet       Period = 13.8 yr
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  14.6   06 18  +58 31   1.964   1.625    93    Lyn
2018-10-11  14.5   06 55  +63 01   1.954   1.561    97    Cam
2018-10-21  14.4   07 38  +67 09   1.948   1.512    99    Cam
2018-10-31  14.4   08 30  +70 40   1.948   1.478   102    UMa
(3552) Don Quixote
T = 2018-May-07  q = 1.24 AU   Extinct comet       Period =  8.8 yr
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-10-01  16.3   02 34  +52 15   2.134   1.405   124    Per
2018-10-11  16.3   02 14  +53 58   2.218   1.433   130    Per
2018-10-21  16.4   01 52  +54 37   2.301   1.480   135    Per
2018-10-31  16.5   01 31  +54 18   2.384   1.548   138    Per

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)

 
 

ALPO COMET NEWS FOR SEPTEMBER 2018

2018-September-3

[Note from the Comet Section Coordinator: For the past few months I have been posting these monthly summaries on the CloudyNights forum. Each monthly ALPO Comet News has its own forum page for observers and comet enthusiasts to share observations. Please check it out and join in the fun if so inclined. Here's a direct link to the September 2018 page.

https://www.cloudynights.com/topic/631971-alpo-comet-news-for-september-2018/ ]

21P/Giacobini-Zinner will be the focus of most comet watchers this month as it peaks at 7th magnitude. Only C/2016 M1 (PANSTARRS) will be brighter than 10th magnitude though it is only in view for southern observers. This fall and winter will see a number of bright short-period comets come into view. CCD and large aperture visual observers will be able to watch 38P/Stephan-Oterma, 46P/Wirtanen and 64P/Swift-Gehrels brighten to around magnitude 11, 11 and 12, respectively. Each will brighten further over the next few months with Wirtanen reaching around 3rd magnitude (though it may be a relatively low surface brightness object).

Bright Comets (magnitude < 10)

21P/Giacobini-Zinner – Short-period comet 21P/Giacobini-Zinner will be this month’s brightest comet. With an orbital period of 6.5 years, 21P is making its 16th observed return since its visual discovery in 1900. This year 21P has an above average return as it will pass 0.39 AU of Earth on September 10 with perihelion also occurring on the that date. Only the returns in 1946 and 1959 were closer to Earth and not until 2078 will 21P be this close again.

Visual observations submitted to the ALPO over the last week or so show 21P to be between magnitude 7.4 and 7.6. This suggests the comet is running a little fainter than expected. Then again the Moon has been bright and/or nearby and possibly hiding the outer extent of 21P’s coma resulting in fainter estimates. Regardless, 21P should start the month close to its peak brightness with a sight fading of ~0.5 magnitudes or so by the end of the month.

With a path that is almost parallel to the Milky Way, 21P will continue to pass through some deep sky rich constellations [Auriga (Sep 1-13), Gemini (13-16,18-19,20-22), Orion (16-18,19-20) and Monoceros (22-31)]. The month starts with G-Z as a far northern object moving past the bright star Capella. It becomes an easier object for southern observers as the month progresses. Close approaches providing nice photo ops will occur on Sep 10th (open cluster M37), 15th (open cluster M35), 22nd through 24th (dark nebulae Barnard 37 and 38 and open cluster NGC 2264, the Christmas Tree Cluster), 26th and 27th (the Rosette Nebula and adjacent open clusters) and 30th (open cluster NGC 2301). Recent images by Chris Schur, Manos Kardasis and Charles Bell continue to show the sunward jet(s) or fan that was mentioned last month.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018- 9-01   7.1   05 00  +48 25   1.022   0.406    80M   Aur
2018- 9-11   7.0   05 52  +32 06   1.013   0.391    79M   Aur
2018- 9-21   7.1   06 27  +14 58   1.024   0.408    81M   Gem
2018-10-01   7.6   06 51  +00 03   1.055   0.453    84M   Mon

The image below is from Manos Kardasis and shows 21P and its sunward fan/jet on August 17.

C/2016 M1 (PANSTARRS) - Visual observations by Chris Wyatt on August 29 found the comet at magnitude 9.8 which is a little fainter than expected. Having passed perihelion on August 10 at 2.21 AU and now moving away from both the Earth and Sun, C/2016 M1 should continue to slowly fade as it moves through the southern reaches of Centaurus.

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01   9.5   14 29  -58 16   2.225   2.144    81E   Cen
2018-09-11   9.7   14 25  -59 11   2.241   2.297    74E   Cen
2018-09-21   9.9   14 24  -60 23   2.263   2.438    68E   Cen
2018-10-01  10.1   14 27  -61 51   2.290   2.564    62E   Cen

Faint Comets (between magnitude 10 and 13)

38P/Stephan-Oterma – Comet Stephan-Oterma is returning for the first time since 1980. This comet has a bit of an interesting backstory. In 1867, it was first sighted by Jérôme E. Coggia (Marseilles, France) who thought he had found an uncatalogued nebula. Over the following nights, followup observations by E. J. M. Stephan (Marseilles, France) uncovered the true nature of the object. For some reason, the discovery announcement cited Stephan as the discoverer with no mention of Coggia. After being missed at its next return in 1904, the comet was photographically rediscovered in 1942 by Liisi Oterma (Turku, Finland).

This month, 38P will be a morning object in Orion as it brightens from 12th to 10th magnitude. Ultimately the comet will peak around magnitude 9.0 to 9.5 in late November after its perihelion on November 10 at 1.59 AU. In 1980, Stephan-Oterma approached to within 0.59 AU of Earth and brightened to between magnitude 8.5 and 9.0. This year’s return will be a little further away at 0.76 AU, hence the slightly fainter maximum brightness.

38P/Stephan-Oterma 
T = 2018-Nov-10  q = 1.59 AU   Short-Period comet  Period = 38.0 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  12.5   04 43  +07 17   1.819   1.548    88M   Ori
2018-09-11  11.9   05 07  +08 44   1.762   1.422    91M   Ori
2018-09-21  11.4   05 31  +10 16   1.713   1.306    94M   Ori
2018-10-01  10.8   05 55  +11 56   1.670   1.199    98M   Ori

46P/Wirtanen – The brightest comet of the year should be 46P/Wirtanen which will pass within 0.08 AU of the Earth in mid-December. Wirtanen will be located around a southern declination of -30 degrees till late November (in the constellations of Cetus and Fornax). The comet will brighten from 14th to 11th magnitude this month.

By late November, it will begin to rapidly move northeastward across Eridanus, Aries, Taurus, Perseus, Auriga, Lynx and Ursa Major. Naked eye brightness should be attained by late November. A peak brightness around magnitude 3 occurs in mid-December. Note, that as a short-period comet, Wirtanen is likely to be a large diffuse object around the time of closest approach. It is possible its coma diameter will be in excess of 1 degree. Do not expect it to appear as bright as a 3rd magnitude star since it light will be spread over a large area. Observers may need a relatively dark sky to see Wirtanen with the naked eye.

46P/Wirtanen
T = 2018-Dec-12  q = 1.06 AU   Short-Period comet  Period = 5.4 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  14.2   01 31  -18 14   1.668   0.781   137M   Cet
2018-09-11  13.2   01 41  -20 33   1.583   0.667   141M   Cet
2018-09-21  12.3   01 48  -23 17   1.500   0.566   143M   Cet
2018-10-01  11.3   01 53  -26 14   1.418   0.479   144M   For

48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.
During August, most observers have been consistently placing this comet between magnitude 12 and 13 The only dissenter being J. J. Gonzalez who estimates a much brighter magnitude of 9.6 to 9.7. J. J. also is seeing a much larger coma (1-2’ vs 7’). It is possible that a very low surface brightness extended coma is being missed by some observers. Now past perihelion the comet should start to fade by ~0.7 magnitudes this month.

48P/Johnson
T = 2018-Aug-12  q = 2.00 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  11.2  +22 35  -27 10   2.011   1.029   161E   PsA
2018-09-11  11.4  +22 31  -28 16   2.019   1.064   154E   PsA
2018-09-21  11.6  +22 28  -28 45   2.029   1.119   145E   PsA
2018-10-01  11.9  +22 28  -28 39   2.043   1.191   137E   PsA

64P/Swift-Gehrels – Comet Swift-Gehrels was originally discovered visually by Lewis Swift (Rochester, New York) in 1889. Swift was also the discoverer of the Perseid parent body, Swift-Tuttle. After the 1889 apparition Swift’s comet went unobserverd until 1973 when its was rediscovered by Tom Gehrels on photographic plates taken at Palomar Observatory in southern California. 2018 marks Swift-Gehrels’ 7th observed return. Since its discovery in 1889, the comet’s orbit has been fairly stable with an orbital period of 9.4 years and perihelion distance near its current value of 1.39 AU. Not an especially bright object, this year’s return will be its best known return with a minimum Earth-comet distance of 0.44 AU on October 28. You will have to wait till 2092 for another return as good as this year’s though the 2046 return will just a little worse.

64P has already shown some excitement with a short lived outburst that saw it brighten by ~2-3 magnitudes to around 13th magnitude in mid-August. Swift-Gehrels has since settled down again and, unless it outbursts again, should brighten from 15th to 12th magnitude this month. Peak brightness will be around magnitude 9.5 in late November.

64P/Swift-Gehrels
T = 2018-Nov-3  q = 1.39 AU   Short-Period comet  Period = 8.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  15.0   00 17  +20 28   1.586   0.663   142M   Psc
2018-09-11  14.0   00 22  +24 20   1.534   0.590   146M   Psc
2018-09-21  13.1   00 25  +28 05   1.489   0.533   149M   Psc
2018-10-01  12.2   00 28  +31 27   1.452   0.491   151M   And

The image below by Charles Bell shows 38P on August 15 during its recent outburst.

C/2016 R2 (PANSTARRS) – CO+ rich comet C/2016 R2 (PANSTARRS) continues its very slow fade. Thanks to its large perihelion distance (2.60 AU), the comet experiences slow changes in its heliocentric and geocentric distances. The comet should remain around 12th magnitude this month as it pulls sway from the Sun in the northern morning sky.

C/2016 R2 (PANSTARRS)
T = 2018-May-02  q = 2.60 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  11.7   10 58  +50 43   2.869   3.532    42M   UMa
2018-09-11  11.8   11 27  +49 40   2.914   3.538    44M   UMa
2018-09-21  11.9   11 56  +48 29   2.962   3.544    47M   UMa
2018-10-01  12.0   12 23  +47 14   3.012   3.552    50M   CVn

C/2017 T3 (ATLAS) – The most recent observation by Chris Wyatt placed Comet ATLAS at magnitude 12.3 on August 29. This is a good magnitude or more fainter than it should be and significantly fainter than it was on August 14 (magnitude 10.2). It will be interesting to see if the comet is really fading fast (or if a bright Moon-lit sky is to blame). Now over a month past perihelion, C/2017 T3 (ATLAS) should be fading though now the question is how rapidly.

C/2017 T3 (ATLAS)
T = 2018-Jul-19  q = 0.83 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  10.8   11 33  -30 51   1.151   1.696    41M   Hya
2018-09-11  11.5   12 21  -30 25   1.276   1.899    38M   Hya
2018-09-21  12.2   12 59  -29 30   1.406   2.114    34M   Hya
2018-10-01  12.8   13 30  -28 28   1.539   2.328    29M   Hya

C/2018 N1 (NEOWISE) - C/2018 N1 (NEOWISE) was discovered by NASA’s low-Earth orbiting NEOWISE spacecraft on July 2nd at 16th magnitude. Earth-based observers quickly determined that NEOWISE was much brighter. The comet continued to brighten as it approached perihelion on August 1 at 1.31 AU and closest to Earth on July 27 at 0.31 AU. Chris Wyatt and Juan Jose Gonzalez estimated it to be around magnitude 8.3 to 9.5 by the end of July. The comet is in full retreat from both the Sun and Earth and should continue to fade from 12th to near 14th magnitude as it recedes back into the outer solar system.

C/2018 N1 (NEOWISE)
T = 2018-Aug-01  q = 1.31 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  12.2   15 12  -10 00   1.383   1.344    70E   Lib
2018-09-11  12.8   15 07  -08 38   1.438   1.660    59E   Lib
2018-09-21  13.3   15 06  -07 47   1.504   1.950    49E   Lib
2018-10-01  13.7   15 07  -07 12   1.580   2.210    40E   Lib

Other Comets of Interest

C/2017 S3 (PANSTARRS) – Last month we left C/2017 S3 (PANSTARRS) in a sad state. Being dynamically new and intrinsically faint, PANSTARRS was expected to disintegrate at some point either on approach to perihelion or not too long afterwards. After experiencing at least two outbursts on June 30/July 1 and July 15, the comet’s morphology and dust/gas production seemed to nosedive on the 20th. The last Earth-based images were taken on August 3rd and showed a diffuse object with no central condensation. As far as anyone could tell the comet’s nucleus had been severely disrupted.

No further Earth based observations were possible after the first few days of August because of the comet’s decreasing elongation from the Sun. Luckily, the comet did travel through the FOV of the Hi1 imager on the STEREO-A spacecraft between July 31 and August 14. Surprisingly the comet was still visible in the STEREO images on the 14th as it was leaving the FOV. For the entire period within the STEREO FOV, the comet appeared elongated and stretched along the direction of its orbit. Currently the comet is now moving through the FOV of the LASCO C3 instrument on the SOHO spacecraft. The SOHO C3 does not go as faint as the STEREO H1A and so far there has been no sign of the comet in that instrument. We will have to wait till sometime in mid to late October to see the comet again from Earth though it is highly unlikely that anything will remain to be seen of C/2017 S3.

(944) Hidalgo and (3552) Don Quixote – Two low activity or extinct comets come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though a tail was seen in 2009 and again this March. This month Don Quixote is near magnitude 16.3. (944) Hidalgo is still inbound and will peak in brightness at 14.3 in November. Unlike Don Quixote, Hidalgo has shown no cometary activity so far.

364P/PANSTARRS – 364P/PANSTARRS is another low activity comet, but only shows activity at small heliocentric distances. Discovered in 2013, 364P is making its second observed return with perihelion having occurred in late June at 0.80 AU. Cometary activity should greatly decrease or even cease allowing CCD imagers the opportunity to directly image its bare nucleus this month at around 17th magnitude.

364P/PANSTARRS
T = 2018-Jun-24  q = 0.80 AU   Short-Period comet  Period =  4.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  16.5   01 32  -32 23   1.309   0.391   133M   Scl
2018-09-11  16.7   00 52  -29 37   1.415   0.463   146M   Scl
2018-09-21  17.0   00 22  -26 28   1.521   0.555   153M   Scl
2018-10-01  17.6   00 02  -23 18   1.625   0.668   153E   Cet
(944) Hidalgo
T = 2018-Oct-26  q = 1.95 AU   Extinct comet       Period = 13.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  15.0   04 53  +44 37   2.025   1.909    81M   Aur
2018-09-11  14.9   05 18  +49 11   2.000   1.801    85M   Aur
2018-09-21  14.7   05 46  +53 51   1.979   1.706    90M   Aur
2018-10-01  14.6   06 18  +58 31   1.964   1.625    93M   Lyn
(3552) Don Quixote
T = 2018-May-07  q = 1.24 AU   Extinct comet       Period =  8.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-09-01  16.3   03 01  +42 32   1.884   1.400   101M   Per
2018-09-11  16.3   02 58  +46 20   1.967   1.392   109M   Per
2018-09-21  16.3   02 49  +49 39   2.051   1.392   116M   Per
2018-10-01  16.3   02 34  +52 15   2.134   1.405   124M   Per

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)

 
 

ALPO COMET NEWS FOR AUGUST 2018

2018-August-1

All eyes were on C/2017 S3 (PANSTARRS) in July as the comet experienced two outbursts and kept observers wondering for how much longer will it survive. As August begins, PANSTARRS is still with us though recent CCD images suggest it is in a weakened or even disrupted state. Luckily, short-period comet 21P/Giacobini-Zinner will provide a nice bright comet to observe this month as it brightens to magnitude 7 by the end of the month.

Bright Comets (magnitude < 10)

21P/Giacobini-ZInner - Assuming C/2017 S3 (PANSTARRS) doesn’t give us another surprise, short-period comet 21P/Giacobini-Zinner should be the brightest comet this August. With an orbital period of 6.5 years, 21P is making its 16th observed return since its visual discovery in 1900 by Michel Giacobini (Nice, France). Though missed at its next return, it was visually re-discovered 2 returns later in 1913 by Ernst Zinner (Bamberg, Germany), hence the double appellation.

This year 21P has an above average return as it will pass 0.39 AU of Earth on September 10 with perihelion also occurs on the that date. Only the returns in 1946 and 1959 were closer to Earth and not until 2078 will 21P be this close again.

21P brightened to magnitude ~8.5 to 9.0 by the end of July and appears to be brightening as expected.. This month the comet continues to ride high in the northern sky. Though best in the morning, it is visible all night long for northern observers. The comet starts the month around magnitude 8.8 and should brighten to 8.0 by the 14th, 7.5 by the 23rd and 7.1 by the end of the month. Visual and CCD observers will enjoy watching 21P pass through the star-rich constellations of Cassiopeia (Aug 1-18), Camelopardalis (18-27), Perseus (27-28) and Auriga (29-31). By the end of the month, 21P will have started to move south enough for some southern hemisphere observers to observe it. September will see its southern motion accelerate allowing observers in both hemispheres an opportunity to enjoy the comet.

CCD images by John D. Sabia from July 12 and 19 show an elongated coma with the beginning of a tail. There also appears to be a sunward feature as well.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01   8.8   23 59  +65 32   1.163   0.593    88M   Cas
2018-08-11   8.2   01 41  +66 19   1.101   0.520    85M   Cas
2018-08-21   7.6   03 31  +61 20   1.054   0.456    82M   Cam
2018-08-31   7.1   04 54  +49 52   1.024   0.410    80M   Aur

C/2016 M1 (PANSTARRS) – Dynamically old, long-period comet C/2016 M1 passes perihelion on August 10 at 2.21 AU. Visual observations by Chris Wyatt and Willian Souza found the comet slowly fading in July from between around magnitude 8.3 – 8.7 to between 8.6 and 9.1. Though it passes perihelion this month, an increasing comet-Earth distance will result in a further fading by another ~0.5 magnitude over the course of the month. As was the case last month, C/2016 M1 is solely a southern hemisphere object this month as it moves through Circinus (Aug 1-19) and Centaurus (19-31).

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet – dynamically old
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01   8.9   15 24  -56 12   2.213   1.640   110E   Cir
2018-08-11   9.1   14 58  -56 57   2.211   1.801    99E   Cir
2018-08-21   9.3   14 40  -57 31   2.214   1.966    90E   Cen
2018-08-31   9.5   14 30  -58 12   2.224   2.128    81E   Cen

C/2017 S3 (PANSTARRS) – Going… going… gone??? The “biggest question mark” of July remains a big question mark in August as well. Dynamically new and intrinsically faint C/2017 S3 (PANSTARRS) was expected to disintegrate at some point either on approach to perihelion or not too long afterwards. Based on recent magnitude estimates and CCD images, the comet may have already disrupted.

But first, let’s recap an exciting July. At the end of June, the comet was less than impressive and rather faint at about 12th magnitude. On June 30 or July 1, the comet experienced its first outburst and ultimately peaked around magnitude 9.0 between July 4th and 7th. CCD images showed a brighter and larger comet but little in the way of near-nucleus structure to suggest a break-up was underway. By July 13th the comet had settled down to magnitude 10. A second outburst started by the 15th and resulted in a peak brightness close to magnitude 7 on the 20th. This time CCD images did detect significant near-nucleus features. Two jets perpendicular to the comet-Sun direction were detected. Jets of this type are sometimes referred to as “wings” and have been interpreted as a sign of nucleus splitting. Not every comet displaying “wings” disintegrated [for example, the great comet C/1996 B2 (Hyakutake) displayed "wings" in Hubble images], but many disintegrating comets have displayed these features in the weeks to days prior to complete disruption [examples include C/1996 Q1 (Tabur), C/1999 S4 (LINEAR) and C/2012 S1 (ISON)].. The “wings” were visible from July 15th to the 20th. On the 20th, I was able to observe the comet at magnitude 7.1. It was as an easy object in 10×50 binolculars and wonderful in my 30×125s.

So far, July 20th has been the peak for this comet. Within hours, the “wings” disappeared and a pronounced drop in brightness was observed. A report by Bernd Lütkenhöner (on the comets-ml) announced that the comet is deviating from its orbit suggest that what is left of the nucleus is small enough (or in small enough pieces) to be very sensitive to the solar radiation pressure.. In effect, these pieces are being “blown” radially away from the Sun relative to where the comet should be, just like comet tail particles. Interestingly, the start of these deviations from the expected position began around the time the second outburst ceased. A recent image by Denis Buczynski on July 30 UT ( http://www.britastro…1_0124_dgb.html ) shows a very diffuse comet with almost no central condensation. This image appears to confirm that the nucleus is either highly or totally disrupted.

Assuming there is anything left of C/2017 S3, perihelion will occur this month on the 15th at a rather small perihelion distance of 0.21 AU. Being only 2 weeks from perihelion, it is already at a small elongation of 31 degrees on the 1st. Most observers will lose sight of it during the first week of August as its elongation drops below 25 degrees on the 4th and 20 degrees on the 6th. If the comet is still a going concern it will be visible in the SOHO LASCO C3 FOV between August 24 and September 13. The comet appear around the 7:30 position, passes to the east (left) of the Sun (halfway between the Sun and edge of FOV) and exits the FOV around the 12:30 position. On July 31, the STEREO Hi1-A camera will also provide continuous imaging of what is left of the comet.

C/2017 S3 (PANSTARRS)
T = 2018-Aug-15  q = 0.21 AU   Long-Period comet – dynamically new
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01   ?.?   06 57  +40 06   0.536   0.810    31M   Aur
2018-08-11   ?.?   08 37  +12 47   0.276   0.800    11M   Cnc
2018-08-21   ?.?   10 06  +01 57   0.279   1.204    10E   Sextens
2018-08-31   ?.?   10 53  +06 40   0.539   1.538     4E   Leo

C/2017 T3 (ATLAS) – Too bad dynamically old, long-period comet C/2017 T3 (ATLAS) wasn’t better placed for observation. A triple whammy of a large geocentric distance, and a small elongation, and only being observable from the southern hemisphere has hindered observation of this comet. Now a few weeks past perihelion, C/2017 T3 (ATLAS) has probably peaked in brightness. Chris Wyatt observed ATLAS throughout July and consistently estimated it to be between magnitude 8.9 and 9.4. Located south of the Sun, the comet will remain visible only from the southern hemisphere and even then at low elevations (~10 – 17 degrees).

C/2017 T3 (ATLAS)
T = 2018-Jul-19  q = 0.83 AU   Long-Period comet – dynamically old
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01   9.0   08 04  -20 10   0.860   1.351    39M   Pup
2018-08-11   9.4   09 16  -26 30   0.930   1.390    41M   Pyx
2018-08-21  10.0   10 27  -29 52   1.026   1.506    42E   Ant
2018-08-31  10.7   11 27  -30 50   1.139   1.677    41E   Hyd

C/2018 N1 (NEOWISE) – C/2018 N1 (NEOSWISE) was discovered by NASA’s low-Earth orbiting NEOWISE spacecraft on July 2nd at 16th magnitude. Earth-based observers quickly determined that NEOWISE was much brighter. The comet continued to brighten as it approached perihelion on August 1 at 1.31 AU and closest to Earth on July 27 at 0.31 AU. Chris Wyatt and Juan Jose Gonzalez estimated it to be around magnitude 8.3 to 9.5 by the end of July. During August the comet will head north again as it moves through Scorpius (Aug 1), Ophiuchus (1-4), Scorpius (4-5), Ophiuchus (5-7), Scorpius (7-10) and Libra (10-31). It will quickly fade as it slowly moves away from the Sun and rapidly away from the Earth.

C/2018 N1 (NEOWISE)
T = 2018-Aug-01  q = 1.31 AU   Long-Period comet – dynamically old
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01   9.1   17 53  -31 38   1.308   0.358   139E   Oph
2018-08-11  10.4   15 57  -18 19   1.315   0.641   102E   Lib
2018-08-21  11.4   15 25  -12 47   1.339   0.977    84E   Lib
2018-08-31  12.1   15 13  -10 11   1.378   1.312    71E   Lib

Faint Comets (between magnitude 10 and 13)

37P/Forbes – Short-period comet Forbes was discovered by South African astronomer Alexander F. I. Forbes on August 1, 1929. 2018 marks the comet’s 15th apparition and 12th observed apparition since discovery. During its last return the comet experienced a 4 magnitude outburst some 9 months after perihelion. This year 37P was not expected to become brighter than ~13th magnitude. Recent observations place the comet anywhere from magnitude 10.5 to 13.5 over the past few weeks. Similar to last month, estimates of coma diameter are also all over the place (from 1′ to 5′) suggesting the comet’s perceived brightness may depend on how much of a low surface brightness coma is being detected by each observer. The magnitudes forecast below are splitting the difference between the late June observations. Located in Pisces, Forbes rises late in the evening.

Similar to 21P’s CCD appearance, Charles Bell found 37P to possess a long anti-solar tail and what appears to be a sunward feature.

37P/Forbes
T = 2018-May-04  q = 1.61 AU   Short-Period comet  Period = 6.4 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  12.4   23 44  +04 03   1.826   0.999   130M   Psc
2018-08-11  12.7   23 41  +05 19   1.872   0.980   139M   Psc
2018-08-21  12.9   23 34  +06 08   1.920   0.976   149M   Psc
2018-08-31  13.2   23 25  +06 29   1.970   0.990   160M   Psc

38P/Stephan-Oterma – Comet Stephan-Oterma is returning for the first time since 1980. This comet has a bit of an interesting backstory. In 1867, it was first sighted by Jérôme E. Coggia (Marseilles, France) who thought he had found an uncatalogued nebula. Over the following nights, followup observations by E. J. M. Stephan (Marseilles, France) uncovered the true nature of the object. For some reason, the discovery announcement cited Stephan as the discoverer with no mention of Coggia. Though Coggia would go on to discover six more comets, 38P was his first. After being missed at its next return in 1904, the comet was photographically rediscovered in 1942 by Liisi Oterma (Turku, Finland).

A side note, Coggia would see his name dropped from another of his discoveries when Comet 1873 V1 (Coggia-Winnecke) was linked with comets 1818 D1 (Pons) and a comet discovered by Forbes in 1928. Comet Pons-Coggia-Winnecke-Forbes was then rebranded 27P/Crommelin after the orbit computer Andrew Claude de la Cherois Crommelin.

Michael Olason and Carl Hergenrother were able to image the comet last month. On July 20th, 38P was measured at magnitude 15.1 which is at its expected brightness. This month, 38P will be a morning object in Taurus as it brightens from 14th to 12th magnitude. Ultimately the comet will peak around magnitude 9.0 to 9.5 in late November after a perihelion on November 10 at 1.59 AU. In 1980, Stephan-Oterma approached to within 0.59 AU of Earth and brightened to between magnitude 8.5 and 9.0. This year’s return will be a little further away at 0.76 AU, hence the slightly fainter maximum brightness.

38P/Stephan-Oterma
T = 2018-Nov-10  q = 1.59 AU   Short-Period comet  Period = 38.0 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  14.4   03 33  +02 52   2.025   1.989    77M   Tau
2018-08-11  13.8   03 55  +04 18   1.954   1.839    80M   Tau
2018-08-21  13.2   04 17  +05 43   1.887   1.696    84M   Tau
2018-08-31  12.6   04 40  +07 08   1.825   1.561    87M   Tau

48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.

Most observers have been consistently placing this comet around magnitude 13.0 which is ~2 magnitudes fainter than expected based on it previous returns. The only dissenter being J. J. Gonzalez who estimates it at the much brighter magnitude of 9..8 to 10.5. J. J. also is seeing a much larger coma (1′ vs 6′), so again there is a question as to whether a very low surface brightness extended coma is being missed by some observers. 48P should peak in brightness this month as it passes through perihelion and opposition.

48P/Johnson
T = 2018-Aug-12  q = 2.00 AU   Short-Period comet  Period = 6.5 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  11.2   22 43  -21 20   2.007   1.055   151M   Aqr
2018-08-11  11.2   22 42  -23 24   2.005   1.024   159M   Aqr
2018-08-21  11.1   22 39  -25 22   2.006   1.014   163M   PsA
2018-08-31  11.2   22 35  -27 02   2.010   1.026   161E   PsA

364P/PANSTARRS – 364P/PANSTARRS is an example of a low activity comet. Similar to other comets of this type (such as 162P/Siding Spring, 169P/NEAT, 209P/LINEAR, 249P/LINEAR and 300P/Catalina), 364P is only active at small heliocentric distances. There is even some research that suggests that some of these objects originated in the Main Belt rather than the Kuiper Belt like most short-period comets.

Discovered in 2013 as P/2013 CU129, 364P is making its second observed return. This comet has a rather short period (4.9 years) and is only active for a few months around perihelion. Perihelion occurred in late June at 0.80 AU from the Sun. While it should rapidly fade this month, this is actually a good thing in that it will allow CCD imagers the opportunity to directly image its bare nucleus by September. While mainly a southern object, it should be visible (though still low) for northern observers by mid-month.

364P/PANSTARRS
T = 2018-Jun-24  q = 0.80 AU   Short-Period comet  Period =  4.9 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  12.9   04 35  -33 56   0.997   0.256    78M   Eri
2018-08-11  14.2   03 25  -35 12   1.092   0.288    98M   For
2018-08-21  15.4   02 26  -34 32   1.194   0.330   115M   For
2018-08-31  16.4   01 36  -32 37   1.299   0.384   132M   Scl

C/2016 R2 (PANSTARRS) – Early 2018’s “blue comet” has remained observable even as it went through solar conjunction due to its path well north of the Sun. Juan Jose Gonzalez observed this comet on July 9th and placed it at magnitude 11.3. Though now three months past perihelion, the comet should continue its slow fade as it steadily climbs higher in the morning sky for northern observers.

C/2016 R2 (PANSTARRS)
T = 2018-May-02  q = 2.60 AU   Long-Period comet – dynamically old
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  11.4   09 21  +52 38   2.748   3.514    35M   UMa
2018-08-11  11.5   09 53  +52 17   2.784   3.520    37M   UMa
2018-08-21  11.6   10 24  +51 40   2.822   3.526    39M   UMa
2018-08-31  11.7   10 55  +50 49   2.864   3.531    42M   UMa

Other Comets of Interest

Two low activity comet come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though Spitzer Space Telescope observations from 2009 showed a faint coma and tail. This month Don Quixote is slowly fading from its peak brightness. (944) Hidalgo is still inbound and will peak in brightness at 14.3 in November. Unlike Don Quixote, Hidalgo has shown no cometary activity so far. Both objects are located close to each other in the morning sky.

(944) Hidalgo
T = 2018-Oct-26  q = 1.95 AU   Extinct comet       Period = 13.8 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  15.4   03 48  +31 45   2.128   2.308    66M   Per
2018-08-11  15.3   04 08  +35 40   2.090   2.171    71M   Per
2018-08-21  15.1   04 28  +39 49   2.057   2.042    76M   Per
2018-08-31  15.0   04 51  +44 10   2.027   1.921    81M   Aur

(3552) Don Quixote
T = 2018-May-07  q = 1.24 AU   Extinct comet       Period =  8.8 yr
Date         Mag    R.A.   Decl.     r       d    Elong  const
2018-08-01  16.2   02 44  +29 03   1.637   1.450    81M   Ari
2018-08-11  16.2   02 53  +33 37   1.714   1.433    87M   Per
2018-08-21  16.2   02 59  +37 59   1.794   1.416    93M   Per
2018-08-31  16.3   03 01  +42 08   1.876   1.402   100M   Per

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)

 
 

ALPO COMET NEWS FOR JULY 2018

2018-July-1

Hello Comet Observers!

This month we may see as many as 4 comets become brighter than 9th magnitude. Two are located at far northern declinations while the other two will only be visible to far southern observers.

Bright Comets (magnitude < 10)

C/2016 M1 (PANSTARRS) – The brightest comet of the past two months was well observed in June as it moved southwestward through Sagittarius and Ara. It was fun to watch it glide through such a globular rich part of the sky. By the end of June visual observers were estimating the comet to be between magnitude 7.7 and 8.7. CCD observations by Raymond Ramlow found a brightness that was closer to the brighter end of the visual range. Visual coma diameters ranged from 4′ to 8′ during the last week of June with CCD coma diameters as large as 13′.

The comet is now located at a declination of -46 degrees, putting it out of range for most northern mid-latitude observers. For southern observers it will be located nearly overhead during the late evening. The comet will start the month near peak brightness but should slowly fade as the month progresses. Although perihelion isn’t till August 10, the fading is due to the comet is currently moving away from Earth.

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01   8.3   17 39  -46 24   2.259   1.301   153E   Ara
2018-07-11   8.4   16 51  -51 31   2.238   1.368   139E   Ara
2018-07-21   8.5   16 05  -54 33   2.223   1.482   124E   Nor
2018-07-31   8.6   15 28  -56 06   2.214   1.625   111E   Cir

C/2017 S3 (PANSTARRS) – This comet is the biggest question mark of the month as it approaches perihelion on August 15 at the small distance of 0.21 AU from the Sun. Its orbit suggests that S3 is a dynamically new comet making its first trip through the inner solar system. Dynamically new comets have a tendency to appear very bright when far from the Sun. The enhanced brightness may be due to extremely volatile ices sublimating at low temperatures when far from the Sun. Analysis of the dust tail of dynamically new and now defunct C/2012 S1 (ISON) found evidence of dust released at distances as great as 100 AU! (Sekanina and Kracht, 2014)

Since discovery S3 has shown little intrinsic brightening. That is until late June. Recent CCD images by Raymond Ramlow found the comet to be magnitude 12.3 on June 26. This is ~2 magnitudes brighter than predicted in last month’s ALPO Comet News. That prediction did come with the caveat that gas-rich comets may brighten at a faster rate as they get closer to the Sun. Whether the current brightness increase is due to the development of a larger gas coma is supported by an increase in CCD detected coma diameter from <1′ to 2.2-2.3′.

Of course the question every one wants answered is how bright will S3 get. Well… it is probably too early to tell. There is not enough data to determine whether the 2 magnitude jump was a sudden event or the start of a new brightening trend. For now the magnitudes below may be very off. I’ll update them as more data comes in. An old saying about forecasting the stock market also applies to comets. “If you’re going to predict, predict often.”

S3 is only a northern hemisphere object as it is located close to and north of the Sun. It is circumpolar for much of the month though it is easier to observe in the morning. All observers are asked to observe this object as often as possible. Not only to watch its brightness trend but also to watch for signs of disintegration. Even after the 2 magnitude bump, dynamically new comets as faint as S3 have a high probability of disintegration as they near the Sun.

C/2017 S3 (PANSTARRS)
T = 2018-Aug-15  q = 0.21 AU   Long-Period comet - dynamically new
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  11.8   03 01  +59 24   1.237   1.562    52M   Cas
2018-07-11  10.7   03 59  +58 25   1.030   1.308    50M   Cam
2018-07-21   9.1   05 14  +54 18   0.807   1.051    45M   Aur
2018-07-31   7.0   06 47  +42 05   0.562   0.827    33M   Aur

C/2017 T3 (ATLAS) - Out of view since April, Comet ATLAS was picked up again visually by Chris Wyatt. He observed the comet to be magnitude 9.4 on June 22nd and 8.8 on the 23rd. Ever since its discovery by the Hawai’i-based ATLAS (Asteroid Terrestrial-impact Last Alert System) project in October of last year, ATLAS has been brightening at a slightly faster than expected rate. The new observations show that it continues to brighten at a slightly faster than normal rate (2.5n ~ 12 compared to 2.5n ~ 10 which is usually, and often incorrectly, assumed for all long-period comets). The rapid brightening is not atypical for a dynamically old comet (one that has been through the inner solar system before).

Perihelion occurs this month on the 19th at 0.83 AU though the comet will be a rather distant 1.4 AU from the Earth at that time. Peak brightness occurs towards the end of this month at between magnitude 8.0 and 8.5. For southern hemisphere observers, the comet will be visible at a low elevations (~10 – 15 degrees). Unfortunately, it will be unobservable for northern hemisphere observers till the very end of the year when it will be a faint object (~16th magnitude).

C/2017 T3 (ATLAS)
T = 2018-Jul-19  q = 0.83 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01   9.0   05 18  +05 24   0.893   1.685    26M   Ori
2018-07-11   8.5   06 00  -02 11   0.840   1.526    31M   Ori
2018-07-21   8.3   06 53  -10 51   0.826   1.406    35M   Mon
2018-07-31   8.3   07 57  -19 23   0.855   1.352    39M   Pup

21P/Giacobini-ZInner – Many long-time observers may remember this comet’s last excellent return in the fall of 1985 just as Comet Halley was approaching its 1986 perihelion. This year marks G-Z’s 16th observed return since its visual discovery in 1900 by Michel Giacobini (Nice, France). The comet was visually re-discovered 2 returns later in 1913 by Ernst Zinner (Bamberg, Germany), hence the double appellation. Perihelion and closest approach to Earth both occur on September 10 at 1.01 AU and 0.39 AU, respectively. This will be the comet’s closest approach to Earth since 1959 when it passed 0.35 AU from Earth.

Recent observations show that 21P has brightened to magnitude 11.0 to 12.0 by the last week in June. This month the comet is high in the morning sky (for northern observers) as it moves through Cygnus, Cepheus and Cassiopeia. It should rapidly brighten from around magnitude 11 to 10 by the midde of the month and 9 by the end of the month. Its current brightening is still consistent with a peak brightness of around magnitude 7 in early September. Though the comet will be located at high northern declinations over the next few months, it will travel far enough south for most southern hemisphere observers by mid-September.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  11.1   21 28  +50 08   1.409   0.849    97M   Cyg
2018-07-11  10.4   21 58  +55 48   1.323   0.762    95M   Cep
2018-07-21   9.6   22 42  +61 05   1.242   0.679    92M   Cep
2018-07-31   8.9   23 50  +65 14   1.169   0.600    88M   Cas

Faint Comets (between magnitude 10 and 13)

37P/Forbes - A new comet to the ALPO Comet News, short-period comet Forbes was discovered by South African astronomer Alexander F. I. Forbes on August 1, 1929. 2018 marks the comet’s 15th apparition and 12th observed apparition since discovery. During its last return the comet experienced a 4 magnitude outburst some 9 months after perihelion. This year 37P was not expected to become brighter than ~13th magnitude. Recent observations place the comet anywhere from magnitude 10.3 to 13.6 over the past few weeks. Estimates of coma diameter are also all over the place (from 1′ to 9′) suggesting the comet’s perceived brightness may depend on how much of a low surface brightness coma is being detected by each observer. The magnitudes forecast below are splitting the difference between the late June observations.

37P/Forbes
T = 2018-May-04  q = 1.61 AU   Short-Period comet  Period = 6.4 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  12.0   23 31  -02 13   1.708   1.117   106M   Psc
2018-07-11  12.1   23 39  +00 07   1.742   1.072   112M   Psc
2018-07-21  12.2   23 44  +02 11   1.780   1.033   120M   Psc
2018-07-31  12.3   23 45  +03 54   1.822   1.002   129M   Psc

48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. The comet should brighten from around magnitude 13 to 12 this month as it moves among the stars of Capricornus in the morning sky. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.

Most observers have been consistently placing this comet around magnitude 14.0 which is ~2 magnitudes fainter than expected based on it previous returns. The only dissenter being J. J. Gonzalez who estimates it at the much brighter magnitude of 11.5. J. J. also is seeing a much larger coma so, again, there is some question as to whether a very low surface brightness extended coma is being missed by some observers.

48P/Johnson
T = 2018-Aug-12  q = 2.00 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  11.9   22 28  -16 26   2.032   1.263   125M   Aqr
2018-07-11  11.6   22 36  -17 38   2.021   1.180   133M   Aqr
2018-07-21  11.4   22 41  -19 14   2.012   1.111   142M   Aqr
2018-07-31  11.3   22 43  -21 08   2.007   1.059   150M   Aqr

66P/du Toit – This marks 66P’s 4th observed and best apparition since its discovery by South African astronomer Daniel du Toit in 1944. Late June observations place the comet between magnitude 11.0 and 11.5. Now that 66P is past its May 19 perihelion, it should start to fade and this may be the last month to catch it visually. A difficult object for northern observers, 66P finally comes into view for those of us at mid-northern latitudes. The next return won’t be till 2033 though with a minimum comet-Earth distance of 1.36 AU it should be a fainter object at that return.

66P/du Toit
T = 2018-May-19  q = 1.29 AU   Short-Period comet  Period = 14.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  12.4   01 03  -22 15   1.410   0.923    93M   Cet
2018-07-11  13.2   01 16  -20 04   1.467   0.924    98M   Cet
2018-07-21  14.1   01 24  -18 15   1.532   0.922   104M   Cet
2018-07-31  15.0   01 26  -16 47   1.604   0.918   111M   Cet

364P/PANSTARRS – 364P/PANSTARRS is an example of a low activity comet. Similar to other comets of this type (such as 162P/Siding Spring, 169P/NEAT, 209P/LINEAR, 249P/LINEAR and 300P/Catalina), 364P is only active at small heliocentric distances. There is even some research that suggests that some of these objects originated in the Main Belt rather than the Kuiper Belt like most short-period comets.

Discovered in 2013 as P/2013 CU129, 364P is making its second observed return. This comet has a rather short period (4.9 years) and is only active for a few months around perihelion. Perihelion occurred last month on the 24th at 0.80 AU from the Sun. Peak brightness will occur a few weeks later closer to the time of closest approach to Earth on July 18 at 0.24 AU. The comet displayed a thin tail in May and June with a hint of a gas coma. Northern observers will be out of luck till early September while southern observers will have an uninterrupted view of the comet (though it will be very low in early July).

364P/PANSTARRS
T = 2018-Jun-24  q = 0.80 AU   Short-Period comet  Period =  4.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  10.9   08 18  -04 58   0.805   0.290    37E   Hya
2018-07-11  10.8   07 23  -17 33   0.842   0.246    39E   CMa
2018-07-21  11.4   06 04  -28 09   0.906   0.236    56M   Col
2018-07-31  12.4   04 42  -33 38   0.988   0.253    76M   Cae

C/2016 R2 (PANSTARRS) – C/2016 R2 passes through solar conjunction this month. Unless C/2016 N6 which will be too close to the Sun to be seen this month, C/2016 R2 will pass sufficiently far enough north of the Sun that it will always remain visible. During the June, the comet was observed between 11 and 12th magnitude. With a distant perihelion on May 2 at 2.60 AU, the comet should slowly fade.

C/2016 R2 (PANSTARRS)
T = 2018-May-02  q = 2.60 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  11.2   07 44  +51 51   2.661   3.476    31E   Lyn
2018-07-11  11.3   08 14  +52 25   2.685   3.493    32E   Lyn
2018-07-21  11.4   08 45  +52 41   2.713   3.504    33M   UMa
2018-07-31  11.4   09 17  +52 39   2.745   3.513    35M   UMa

Other Comets of Interest

Two low activity comet come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though Spitzer Space Telescope observations from 2009 showed a faint coma and tail. This month Don Quixote is slowly fading from its peak brightness. (944) Hidalgo is still inbound and will peak in brightness at 14.3 in November. Unlike Don Quixote, Hidalgo has shown no cometary activity so far. Both objects are located close to each other in the morning sky.

(944) Hidalgo
T = 2018-Oct-26  q = 1.95 AU   Extinct comet       Period = 13.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  15.8   02 54  +20 49   2.263   2.749    51M   Ari
2018-07-11  15.7   03 11  +24 09   2.216   2.606    56M   Ari
2018-07-21  15.5   03 28  +27 40   2.172   2.463    61M   Ari
2018-07-31  15.4   03 46  +31 22   2.131   2.322    66M   Per
(3552) Don Quixote
T = 2018-May-07  q = 1.24 AU   Short-Period comet  Period =  8.8 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-07-01  16.0   02 01  +13 44   1.422   1.493    65M   Ari
2018-07-11  16.1   02 17  +18 53   1.485   1.482    70M   Ari
2018-07-21  16.2   02 31  +23 50   1.555   1.468    75M   Ari
2018-07-31  16.2   02 43  +28 35   1.629   1.452    80M   Ari

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)

 
 

ALPO COMET NEWS FOR JUNE 2018

2018-June-1

Hello Comet Observers!

After a few months of no bright comets, May brought a 9th magnitude comet in C/2016 M1 (PANSTARRS). This comet should continue to be the brightest this month though C/2017 T3 (ATLAS) may challenge it.

Bright Comets (magnitude < 10)

C/2016 M1 (PANSTARRS) – This dynamically old long-period comet was well observed in May with observers reporting it between magnitude 8.5 and 9.6 during the past week. It should continue to brighten by another 0.5 magnitudes this month as it approaches an August 10 perihelion at 2.21 AU. Increasing distance from the Earth after closest approach on June 24 at 1.29 AU will cause a slow fade beginning in late June.

Visual observations found the comet to have a fairly condensed coma (DC between 3 and 5) with a diameter between 3′and 5′. No visual reports of a tail have been made though the coma was observed to be slightly elongated.

The comet’s 91 degree inclination orbit is resulting in a steady southward motion from a June 1 declination of -24 degrees to -46 at the end of the month. It will be seen moving among the stars of Sagittarius, Corona Australis and Ara. A few close approaches to deep space objects will occur this month (Jun 9 – globular cluster M54 and Jun 12/13 – globular cluster M70).

C/2016 M1 (PANSTARRS)
T = 2018-Aug-10  q = 2.21 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01   9.2   19 15  -24 24   2.353   1.463   142M   Sgr
2018-06-11   8.9   18 53  -31 41   2.317   1.349   156M   Sgr
2018-06-21   8.8   18 21  -39 26   2.285   1.293   163M   CrA
2018-07-01   8.7   17 39  -46 24   2.259   1.301   153E   Ara

C/2017 T1 (ATLAS) – It is questionable whether or not this comet will be observable and, if so, how bright it will be this month. C/2017 T1 (ATLAS) was discovered by the Hawai’i-based ATLAS (Asteroid Terrestrial-impact Last Alert System) project on October 14, 2017 at 18th magnitude. At the time the comet was located 4.0 AU from the Sun.

A dynamically-old short-period comet, ATLAS was brightening at a slightly faster than expected rate (2.5n ~ 11 compared to 2.5n ~ 10 which is usually, and often incorrectly, assumed for all long-period comets). This month, southern hemisphere observers may be able to reacquire the comet as it slowly moves away from the Sun in the morning sky. Since the comet has been out of view since April, its currently brightness is uncertain. Assuming (and we know the old saying about making assumptions) the comet has continued to brighten at its pre-April rate, the comet may be as bright as magnitude 9.4 by the end of the month.

Perihelion occurs on July 19 at 0.83 AU though the comet will be a rather distant 1.4 AU from the Earth at that time. With the same caveat about the assumption made above, the comet may peak around magnitude 8.6 around the time of perihelion. For southern hemisphere observers, the comet will be visible at a low elevations (~10 – 15 degrees in July). Unfortunately, it will be unobservable for northern hemisphere observers till the very end of the year when it will be a faint object (~16th magnitude).

C/2017 T3 (ATLAS)
T = 2018-Jul-19  q = 0.83 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  11.4   03 47  +20 43   1.204   2.184    10M   Tau
2018-06-11  10.7   04 14  +16 40   1.084   2.026    15M   Tau
2018-06-21  10.0   04 44  +11 39   0.978   1.857    20M   Ori
2018-07-01   9.4   05 18  +05 24   0.893   1.685    26M   Ori

Faint Comets (between magnitude 10 and 13)

21P/Giacobini-Zinner – Many long-time observers may remember this comet’s last excellent return in the fall of 1985 just as Comet Halley was approaching its February 1986 perihelion. This year marks G-Z’s 16th observed return since its visual discovery in 1900 by Michel Giacobini (Nice, France). The comet was visually re-discovered 2 returns later in 1913 by Ernst Zinner (Bamberg, Germany), hence the double appellation. Perihelion and closest approach to Earth both occur on September 10 at 1.01 AU and 0.39 AU, respectively. This will be the comet’s closest approach to Earth since 1959 when it passed 0.35 AU from Earth.

Recent observations place 21P between magnitude 13.8 and 15.1 over the last week of May. This month the comet is high in the morning sky (for northern observers) as it moves through Cygnus. It should rapidly brighten from around magnitude 13 to 11 over the course of the month. A peak brightness of around magnitude 7 is predicted for early September. Though the comet will be located at high northern declinations over the next few months, it will travel far enough south for most southern hemisphere observers by mid-September.

21P/Giacobini-Zinner
T = 2018-Sep-10  q = 1.01 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  13.2   20 29  +33 15   1.682   1.157   101M   Cyg
2018-06-11  12.5   20 46  +38 43   1.590   1.045   100M   Cyg
2018-06-21  11.8   21 05  +44 23   1.498   0.943    99M   Cyg
2018-07-01  11.1   21 28  +50 08   1.409   0.849    97M   Cyg

48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. The comet should brighten from around magnitude 13 to 12 this month as it moves among the stars of Capricornus in the morning sky. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.

The brightest report from May was by the Catalina Sky Survey which placed Johnson at magnitude 14.8 on May 21. This is about 1.5 magnitudes fainter than the predicted magnitude. If the comet continues to run fainter than predicted, the magnitudes below may be too bright.

48P/Johnson
T = 2018-Aug-12  q = 2.00 AU   Short-Period comet  Period = 6.5 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  12.9   21 53  -14 58   2.084   1.580   104M   Cap
2018-06-11  12.6   22 07  -15 08   2.064   1.465   111M   Aqr
2018-06-21  12.2   22 19  -15 36   2.047   1.359   118M   Aqr
2018-07-01  11.9   22 28  -16 26   2.032   1.263   125M   Aqr

66P/du Toit – Short-period comet 66P/du Toit is still running brighter than predicted. Observers have been estimating it to be between magnitude 10.2 and 10.7 during the last week of May. The comet possesses a large, low surface brightness coma so the comet may appear fainter than expected to some observers. The comet remains a very difficult object for northern hemisphere observers. Personally, I have not been able to acquire it in my 30×125 binoculars due to a combination of its low elevation and a brightening dawn sky. This marks 66P’s 4th observed and best apparition since its discovery by South African astronomer Daniel du Toit in 1944. The next return won’t be till 2033 though with a minimum comet-Earth distance of 1.36 AU it should be a fainter object at that return.

66P/du Toit
T = 2018-May-19  q = 1.29 AU   Short-Period comet  Period = 14.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  10.7   23 54  -30 48   1.302   0.903    85M   Scl
2018-06-11  11.1   00 23  -27 41   1.326   0.911    86M   Scl
2018-06-21  11.7   00 46  -24 49   1.363   0.918    89M   Scl
2018-07-01  12.4   01 03  -22 15   1.410   0.923    93M   Cet

364P/PANSTARRS – 364P/PANSTARRS is an example of a low activity comet. Similar to other comets of this type (such as 169P/NEAT, 249P/LINEAR and 300P/Catalina), 364P is only active at small heliocentric distances. Whether this is due to age, evolution or the possibility that these objects originated in the asteroid Main Belt rather than the Kuiper Belt, is still TBD.

Discovered in 2013 as P/2013 CU129, it is making its second observed return. This comet has a rather short period (4.9 years) and is only active for a few months around perihelion. Perihelion occurs this month on the 24th at 0.80 AU from the Sun. The comet displayed a thin tail in May though it didn’t possess much of a coma. CCD and large aperture visual observers can watch the comet approach and pass through perihelion this month. Northern observers will lose sight of the comet mid-month (regaining the comet in early September) while southern observers will have an uninterrupted view of the comet (though it will get very low in early July).

364P/PANSTARRS
T = 2018-Jun-24  q = 0.80 AU   Short-Period comet  Period =  4.9 yr
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  13.7   08 55  +20 08   0.883   0.530    60E   Cnc
2018-06-11  12.5   08 56  +13 55   0.827   0.447    52E   Cnc
2018-06-21  11.5   08 47  +05 45   0.800   0.362    44E   Hya
2018-07-01  10.9   08 18  -04 58   0.805   0.290    37E   Hya

C/2016 N6 (PANSTARRS) and C/2016 R2 (PANSTARRS) – In addition to C/2016 M1, there are two other PANSTARRS long-period comets with relatively large perihelion distances visible this month. Both are early evening objects located north of the ecliptic. C/2016 R2 passed perihelion on May 2 at 2.60 AU. It is approaching solar conjunction this month though its location north of the ecliptic means it should remain observable though at low elevations through conjunction. C/2016 N6 reaches perihelion on July 18 at 2.67 AU. The comet will be become a more difficult object to observe as the month progresses and should be lost to most observers towards the end of the month. C/2016 R2 will spend the month around magnitude 11 while C/2016 N6 will be around magnitude 12.

C/2016 R2 (PANSTARRS)
T = 2018-May-02  q = 2.60 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  11.1   06 22  +48 36   2.613   3.389    34E   Aur
2018-06-11  11.1   06 47  +49 55   2.625   3.426    32E   Lyn
2018-06-21  11.2   07 15  +51 00   2.641   3.455    31E   Lyn
2018-07-01  11.2   07 44  +51 51   2.661   3.476    31E   Lyn

C/2016 N6 (PANSTARRS)
T = 2018-Jul-18  q = 2.67 AU   Long-Period comet - dynamically old
    Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  12.0   07 56  +46 08   2.715   3.297    47E   Lyn
2018-06-11  12.1   08 02  +42 39   2.698   3.401    39E   Lyn
2018-06-21  12.1   08 08  +39 25   2.684   3.491    32E   Lyn
2018-07-01  12.1   08 15  +36 23   2.675   3.565    24E   Lyn

Other Comets of Interest

Low activity comet (3552) Don Quixote is still designated an asteroid even though Spitzer Space Telescope observations from 2009 showed a faint coma and tail. This month Don Quixote is near its 2018 peak at around 16th magnitude. The object is steadily moving north in the morning sky and is now observable by observers at northern mid-latitudes.

(3552) Don Quixote
T = 2018-May-07 q = 1.24 AU Short-Period comet Period = 8.8 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 15.9 01 04 -02 58 1.280 1.511 56M Cet
2018-06-11 15.9 01 25 +02 48 1.317 1.507 59M Psc
2018-06-21 16.0 01 44 +08 22 1.365 1.501 62M Psc
2018-07-01 16.0 02 01 +13 44 1.422 1.493 65M Ari

Looking ahead, the later months of 2018 will see a few other comets reaching magnitude 10 or brighter. 38P/Stephan-Oterma was observed back in the summer of 2017 by Pan-STARRS at 21st magnitude. CCD observers have recently observed it at 17th magnitude now that it is coming out of solar conjunction. 64P/Swift-Gehrels was detected for the first time this apparition by Spacewatch on May 25 UT at magnitude 20.7. What should be this year’s brightest comet, 46P/Wirtanen, was picked up by the Discovery Channel Telescope on May 8 UT at magnitude 20.3.

Dynamically new and intrinsically faint C/2017 S3 (PANSTARRS) has shown a very slow intrinsic brightening since its September 2017 discovery (2.5n ~ 5.5!). Perihelion occurs on August 15 at a small distance of 0.21 AU. Though the comet will be located too close to the Sun at that time, there is hope it could become bright (7th-8th magnitude) before becoming lost in the glare of the Sun. In mid-May the comet brightened to 15-16th magnitude. Extrapolating it’s slow brightening trend suggests the comet will not be a bright visual object prior to becoming lost in the bright twilight sky. Then again the comet may brighten at a faster rate, especially if gas-rich, as it gets closer to the Sun. A major question remains as to whether it will be a bright visual object prior to perihelion. Being intrinsically faint and dynamically new there is also a real possibility that this comet’s nucleus is small and will disintegrate at it nears the Sun.

C/2017 S3 (PANSTARRS)
T = 2018-Aug-15  q = 0.21 AU   Long-Period comet - dynamically new
Date     Mag    R.A.   Decl.     r       d    Elong  const
2018-06-01  15.7   01 09  +57 25   1.788   2.242    51M   Cas
2018-06-11  15.3   01 40  +58 23   1.614   2.030    51M   Cas
2018-06-21  14.7   02 16  +59 09   1.430   1.803    52M   Cas
2018-07-01  14.1   03 01  +59 24   1.237   1.562    52M   Cas

As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.

- Carl Hergenrother (ALPO Comet Section Coordinator)

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