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ALPO Comet News for September 2018

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#1 Carl H.

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Posted 03 September 2018 - 04:08 AM

ALPO COMET NEWS FOR SEPTEMBER 2018
 
2018-September-3
 
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 

 
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 

 

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)


  • Tonk, happylimpet, roelb and 5 others like this

#2 Carl H.

Carl H.

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Posted 11 September 2018 - 11:09 AM

21P has been fun to watch as it rapidly moves among the open clusters of Auriga. Its tail is obvious in 30x125 binoculars and there, but subtle, in 10x50s.

 

21P/Giacobini-Zinner

2018 Sep 11.43 UT: m1= 7.1, Dia.=9'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 07.41 UT: m1= 7.1, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 05.48 UT: m1= 7.3, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 04.48 UT: m1= 7.2, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 01.48 UT: m1= 7.4, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Aug 28.41 UT: m1= 7.6, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)



#3 Carl H.

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Posted 14 September 2018 - 03:57 PM

Reminder that tonight, 21P will move across the bright open star cluster M35 in Gemini. The comet will be closest to the center of M35 around 4:00 UT though it will be within the boundaries of the cluster for 2-3 hours on either side of that time.

 

As exciting as this will be, the cluster is larger and brighter than the comet and may be very difficult to discern the two with small instruments. Based on my view of both last night in 10x50s, I'm actually wondering if the comet will even be seen superimposed on M35 in binoculars that small. An instrument large enough to resolve M35 should do a better job. I'll be trying in my 30x125s and C14.

 

CCD imagers should have no problem getting nice images of the pair.



#4 Carl H.

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Posted 16 September 2018 - 03:34 PM

Here's my summary of the 21P + M35 conjunction:

 

In 10x50:

At ~09:30 UT, I could see no hint of 21P as it was completely swamped by M35.

 

In a C14:

At 97X, the coma of 21P was obvious among the stars of M35. While there was a hint of a tail, the stars of M35 seemed to drown out most of what could have been seen of 21P.



#5 Raymond Ramlow

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Posted 19 September 2018 - 06:41 PM

I imaged several comets last night (2018 09 19.41-42) with T14. 

 

46P/Wirtanen - much brighter and larger than it was a week ago (11.9 mag and almost 7' as opposed to 12.7 mag and 4' on 2018 07 12.45) under similar conditions.

38P/Stephan-Oterma - not much change from last week (11.5 mag and 6' vs 11.8 mag and 5' on 2018 07 12.46). It seems the very faint outer coma is being missed by most visual observers.

21P/Giacobini-Zinner - faded roughly 0.2 magnitudes since the 12th



#6 Carl H.

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Posted 24 September 2018 - 07:35 PM

The bright Moon will probably keep me from observing 21P for a few nights. Over the past ~2 weeks, 21P seems to have faded slightly from a peak around magnitude 7.0. 

 

21P/Giacobini-Zinner

2018 Sep 22.45 UT: m1= 7.3, Dia.=7'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 18.50 UT: m1= 7.3, Dia.=9'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 17.48 UT: m1= 7.1, Dia.=9'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 14.48 UT: m1= 7.0, Dia.=9'; 10x50 B; Carl Hergenrother (Tucson, AZ)

2018 Sep 12.47 UT: m1= 7.0, Dia.=8'; 10x50 B; Carl Hergenrother (Tucson, AZ)




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