Comets « Comet Section

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.

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
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

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

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

- Carl Hergenrother (ALPO Comet Section Coordinator)

ALPO COMET NEWS FOR MAY 2018

2018-May-1

Hello Comet Observers!

May brings our first comet brighter than magnitude 10 since January as C/2016 M1 (PANSTARRS) should brighten to 9th magnitude. An assortment of short- and long-period comets will be between 10th and 12th magnitude this month as well. Also provided are updates on other comets expected to become bright later this year.

Bright Comets (magnitude < 10)

C/2016 M1 (PANSTARRS) – For the first time since January, a comet is predicted to become brighter than magnitude 10. C/2016 M1 was discovered by the Maui, Hawaii based Pan-STARRS survey on June 22, 2016. At that time the comet was 19th magnitude and located 7.7 AU from the Sun. Since then the comet has brightened to between magnitude 9.9 and 10.8 as reported over the past week. C/2016 M1 is still inbound to a August 10 perihelion at 2.21 AU and should brighten by another magnitude this month to between magnitude 9.0 and 9.5. Due to its 91 degree inclination orbit, the comet will be moving slowly southward from a May 1st declination of -9 degrees to -23 at the end of the month. It will continue to brighten into June though it will become a more difficult object for northern observers as it moves south.

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 rapidly 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. G-Z may be too faint for visual observation this month. CCD imagers can watch it brighten from 15th to 13th magnitude this month. It will continue to brighten and peak around magnitude 7 in early September.

48P/Johnson - 48P/Johnson has a rather large perihelion distance (2.00 AU) for a (relatively) bright short-period comet. Perihelion 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.

66P/du Toit - The month’s brightest short-period comet appears to be running brighter than predicted. Visual observers have been estimating it to be between magnitude 11 and 12 while CCD imagers have it as bright as magnitude 10. It is possible that CCD imagers are detecting a large faint gaseous coma that is being missed visually. Even though my prediction below has the comet brightening to magnitude 10.3 around its May 19 perihelion (at 1.29 AU from the Sun), the comet may look fainter to most observers. Northern observers may have issues observing du Toit as it is still located far south at declinations of -39 to -31 degrees. This marks 66P’s 4th observed and best apparition since its discovery in 1944 by South African astronomer Daniel du Toit.

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 passes perihelion on May 2 at 2.60 AU. It approaching solar conjunction though its location well 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. C/2016 R2 will spend the month between magnitude 11 and 12 while C/2016 N6 will be between 12 and 13.

C/2017 T3 (ATLAS) – Comet Atlas will not be observable from the ground this month as it will be too close to the Sun. It will once again become visible in late June / early July from the southern hemisphere as a 8th-9th magnitude object.

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
2018-05-01  11.6   05 15  +43 26   2.604   3.217    44E   Aur
2018-05-11  11.7   05 34  +45 15   2.602   3.283    40E   Aur
2018-05-21  11.7   05 56  +46 56   2.605   3.339    37E   Aur
2018-05-31  11.8   06 19  +48 28   2.612   3.385    34E   Aur

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
2018-05-01  12.3   07 48  +59 03   2.792   2.940    71E   Lyn
2018-05-11  12.3   07 48  +54 30   2.763   3.056    63E   Lyn
2018-05-21  12.4   07 51  +50 20   2.738   3.173    55E   Lyn
2018-05-31  12.4   07 56  +46 30   2.717   3.286    48E   Lyn

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
2018-05-01  15.1   19 41  +18 33   1.969   1.578    96M   Sge
2018-05-11  14.5   19 56  +22 52   1.877   1.430    99M   Vul
2018-05-21  13.9   20 11  +27 36   1.784   1.293   100M   Vul
2018-05-31  13.3   20 27  +32 43   1.692   1.169   101M   Cyg

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
2018-05- 1  10.1   19 42  -09 22   2.495   2.048   104M   Aql
2018-05-11   9.8   19 38  -13 00   2.445   1.835   115M   Sgr
2018-05-21   9.5   19 31  -17 44   2.399   1.641   127M   Sgr
2018-05-31   9.2   19 17  -23 44   2.357   1.477   141M   Sgr

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
2018-05-01  14.2   21 04  -15 45   2.161   1.974    86M   Cap
2018-05-11  13.8   21 21  -15 21   2.133   1.842    92M   Cap
2018-05-21  13.4   21 37  -15 04   2.108   1.714    98M   Cap
2018-05-31  13.0   21 52  -14 58   2.086   1.592   104M   Cap

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
2018-05-01  10.7   21 42  -39 02   1.313   0.912    86M   Gru
2018-05-11  10.4   22 32  -37 00   1.295   0.898    85M   Gru
2018-05-21  10.3   23 15  -34 13   1.290   0.896    84M   Scl
2018-05-31  10.5   23 51  -31 07   1.300   0.902    85M   Scl

Other Comets of Interest

In last month’s ALPO Comet News, two low-activity comets were introduced. The first, (3552) Don Quixote, is still designated as 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 through Aquarius and Cetus in the morning sky.

The other object is low-activity comet 364P/PANSTARRS. Discovered in 2013, 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. It is similar to other usually inactive comets that are only active near or within 1 AU of the Sun (such as 169P/NEAT, 249P/LINEAR and 300P/Catalina). This year perihelion occurs on June 24. If its activity is similar to 2013’s, May should see 364P’s activity ramping up resulting in a 17th magnitude object at the start of the month brightening to 14th magnitude by month’s end.

(3553) 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
2018-05-01  15.8   23 48  -21 37   1.243   1.528    54M   Aqr
2018-05-11  15.8   00 16  -15 34   1.241   1.520    55M   Cet
2018-05-21  15.8   00 40  -09 31   1.252   1.515    55M   Cet
2018-05-31  15.9   01 02  -03 33   1.277   1.511    56M   Cet

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
2018-05-01  17.3   08 36  +32 39   1.160   0.712    82E   Cnc
2018-05-11  16.3   08 41  +29 23   1.060   0.668    75E   Cnc
2018-05-21  15.1   08 48  +25 28   0.968   0.611    68E   Cnc
2018-05-31  13.8   08 55  +20 40   0.890   0.538    61E   Cnc

The later part of 2018 will see a few other comets reaching magnitude 10 or brighter. So far no observations have been published for 38P/Stephens-Oterma (peak around 9th mag in Nov/Dec) and 64P/Swift-Gehrels (peak around 10th magnitude in Oct/Nov) by the Minor Planet Center. In the case of 38P this is because it has been close to the Sun though the first observations should come in this month (though still fainter than 18th magnitude). 64P must be fainter than 20th magnitude to not have been seen yet.

Dynamically new and intrinsically faint C/2017 S3 (PANSTARRS) has shown a very slow intrinsic brightening since its September 2017 discovery. It will reach a small perihelion distance of 0.21 AU on August 15. Though the comet will be located too close to the Sun at that time, the hope was it would become bright (7th-8th magnitude) before becoming lost in the glare of the Sun. So far the comet has brightened to 17-18th magnitude so there is still some question as to whether it will be a visual object prior to perihelion. Being intrinsically faint and dynamically new there is also a real possibility that this comet is small and will disintegrate at it nears the Sun.

- Carl Hergenrother (ALPO Comet Section Coordinator)

ALPO COMET NEWS FOR MARCH 2018

2018-March-03

Will March be a good month of comet observing? The answer depends on the aperture of your telescope and whether you are a visual or CCD observer. The bad news, unless a surprise discovery or outburst occurs, is that no comet this month will be an easy object for small telescope visual observers. The good news is large aperture visual observers and CCD imagers have quite the varied selection of objects to observe.

This month I decided to try a different format for these monthly summaries. I’m hoping the new format makes it easier to quickly identify observing targets. The comets will be broken down into three categories: comets brighter than magnitude 10, comets between magnitudes 10 and 13, and fainter comets of interest. In some cases, the comet of interest may no longer be visible but is the subject of recent research such as this month’s discussion of long-lost (or is it?) D/1770 L1 (Lexell).

Information for each comet is now presented in tabular form. This information includes the comet’s designation and name, date of perihelion (T), perihelion distance (q), and type of orbit (JFC for Jupiter family comet with period, HFC for Halley family comet with period, LPC-DO for dynamically old long-period comet, LPC-DN for dynamically new long-period comet). At 10 day intervals, the predicted magnitude, rough J2000 RA and Dec position, heliocentric distance, geocentric distance, elongations from the Sun (E for evening object, M for morning object) and constellation is shown.

Bright Comets (magnitude less than 10)

C/2017 T1 (Henize) – This intrinsically faint comet appears to have survived long enough to reach its February 21 perihelion passage at a rather small 0.58 AU from the Sun. As additional astrometric observations were made, the Minor Planet Center orbits for Heinze oscillated between a dynamically old and dynamically new solution. The latest orbit (released on Feb 28 with positions extending through Feb 12) shows Heinze to be dynamically new. Intrinsically faint, dynamically new objects are prone to fade rapidly after perihelion or even completely disintegrate. This is definitely a comet to keep an eye on. Unfortunately that won’t be easy as the comet starts the month close to the Sun. By the 2nd half of the month, Heinze will be far enough away from the Sun to be more easily seen though by then it may be a difficult visual object and also only visible from the southern hemisphere at that time.

C/2017 T1 (Heinze)      T = 2018-Feb-21  q = 0.58 AU	LPC-DN
Date       Mag     RA    DEC     r   delta  elong const
March 01    10   21 36 +10 19   0.60  1.32   25M   Peg
March 11    11   21 39 +03 17   0.69  1.40   27M   Aqr
March 21    12   21 45 -03 31   0.83  1.43   34M   Aqr
March 31    13   21 53 -10 13   0.98  1.43   43M   Cap

Faint Comets (between magnitude 10 and 13)

While there may not be any comet brighter than 10th magnitude this month, there are quite a few comets between magnitudes 10 and 13. In fact, there are seven comets in that brightness range.

C/2016 R2 (PANSTARRS) – The highlight of the bunch remains the ‘blue comet’. No not the famed Jersey Central passenger train, but comet C/2016 R2 (PANSTARRS). This comet is rich in CO+, or the carbon monoxide ion, which gives it a dynamic ion tail and blue color. The comet is still approaching its May 2nd perihelion. Its increasing comet-Earth distance will more than counter the shrinking heliocentric distance so a slow fade should occur this month. Recent magnitude estimates are still scattered but seem to be around 10th to 11th magnitude.

C/2015 O1 (PANSTARRS), C/2015 M1 (PANSTARRS), C/2016 N6 (PANSTARRS) – These three comets are similar to C/2016 R2 in that they are all PANSTARRS discoveries and have relatively large perihelion distances at 3.73, 2.21 and 2.67 AU, respectively. Recent observations place M1 at around magnitude 11 to 12.6. The other two are in the 12th to 13th magnitude range. O1 (for part of the month) and N6 (for the entire month) are northern circumpolar objects so both will be invisible for southern hemisphere observers.

62P/Tsuchinshan and 185P/Petriew – Both of these comets are now past perihelion. Making its 4th observed return, 185P/Petriew is now over a month past perihelion and slowly fading from 12th to 13th magnitude in the evening sky. 62P/Tsuchinshan should be fainter as it fades from 13th to 14th magnitude.

66P/du Toit – This year brings the 4th observed return of 66P/du Toit. Discovered in 1944 by South African astronomer Daniel du Toit, the comet was also seen at its returns in 1974 and 2003 but missed in 1959 and 1988. It is currently on an orbit with a 14.7 year period. This return will see its closest approach to Earth since its 1944 discovery apparition. The comet-Earth distance will still be a rather distant 0.90 AU. As a result, 66P may only brighten to 11th-12th magnitude. During its 2003 return, it rapidly brightened in the months prior to perihelion so this month may see the comet start at 17th magnitude and then brighten to 13th magnitude by month’s end. It will be a difficult object for northern observers due to its southern declination.

185P/Petriew T = 2018-Jan-27  q = 0.93 AU JFC  P = 5.5 yr
Date       Mag     RA    DEC     r   delta  elong const
March 01    12   02 04 +04 31   1.04  1.34   50E   Psc
March 11    12   02 52 +06 52   1.11  1.38   52E   Cet
March 21    12   03 28 +08 49   1.19  1.45   54E   Tau
March 31    13   04 21 +10 18   1.28  1.54   55E   Tau

C/2016 R2 (PANSTARRS) T = 2018-May-02  q = 2.60 AU   LPC-DO
Date       Mag     RA    DEC     r   delta  elong const
March 01    10   04 03 +30 20   2.71  2.61   84E   Tau
March 11    10   04 09 +32 42   2.68  2.72   76E   Per
March 21    11   04 18 +34 59   2.66  2.84   69E   Per
March 31    11   04 29 +37 11   2.64  2.95   62E   Per

C/2016 N6 (PANSTARRS)   T = 2018-Jul-18  q = 2.67 AU    LPC-DO
Date       Mag     RA    DEC     r   delta  elong const
March 01    12   15 15 +77 36   3.03  2.62  105E   UMi
March 11    12   12 19 +80 20   2.98  2.60  103E   Cam
March 21    12   10 01 +79 03   2.94  2.61   99E   Dra
March 31    12   08 43 +74 49   2.90  2.65   93E   Cam

62P/Tsuchinshan         T = 2017-Nov-16  q = 1.28 AU JFC  P = 6.4 yr
Date       Mag     RA    DEC     r   delta  elong const
March 01    13   14 33 +02 35   1.78  1.04  123M   Vir
March 11    13   14 31 +03 22   1.85  1.02  133M   Vir
March 21    14   14 26 +04 11   1.92  1.02  143N   Vir
March 31    14   14 17 +04 54   1.98  1.04  153M   Vir

C/2015 O1 (PANSTARRS)   T = 2018-Feb-19  q = 3.73 AU    LPC-DN
Date       Mag     RA    DEC     r   delta  elong const
March 01    12   16 25 +39 11   3.73  3.44   99M   Her
March 11    12   16 14 +43 03   3.73  3.34  105M   Her
March 21    12   15 58 +46 56   3.73  3.27  110M   Her
March 31    12   15 37 +50 33   3.74  3.23  113M   Boo

66P/du Toit             T = 2018-May-19  q = 1.29 AU    JFC  P = 14.9 yr
Date       Mag     RA    DEC     r   delta  elong const
March 01    17   16 54 -29 02   1.65  1.41   84M   Oph
March 11    16   17 29 -32 11   1.57  1.28   86M   Sco
March 21    15   18 10 -35 10   1.50  1.16   88M   Sgr
March 31    13   18 57 -37 41   1.44  1.07   88M   CrA

C/2016 M1 (PANSTARRS)   T = 2018-Aug-10  q = 2.21 AU    LPC-DO
Date       Mag     RA    DEC     r   delta  elong const
March 01    11   19 14 +01 10   2.86  3.33   53M   Aql
March 11    11   19 22 +00 04   2.80  3.15   60M   Aql
March 21    11   19 29 -01 07   2.73  2.94   67M   Aql
March 31    11   19 35 -02 31   2.67  2.73   75M   Aql

Other Comets of Interest

D/1770 L1 (Lexell) – This comet holds a few distinctions. One, it was the first Jupiter family comet to be recognized as such. Two, it holds the record for closest observed cometary approach to Earth at 0.015 AU or 5.8 lunar distances. Three, it was named not after its discoverer but its orbit computer (similar to 1P/Halley, 2P/Encke and 27P/Crommelin). Four, it was discovered by famed French comet hunter Charles Messier. Five, it hasn’t been seen since.

Quan-Zhi Ye (Caltech), Paul A. Wiegert (Western Ontario) and Man-To Hui (UCLA) have recently published their investigation into the whereabouts of Comet Lexell. They found that even though the comet has experienced numerous close approaches to Jupiter, there is a high probability that the comet still has a perihelion distance of < 3 AU and a close to even probability of having a perihelion distance of < 1 AU. A search of known comets turned up no possible linkages to Lexell but a search of known near-Earth asteroids did find a few possibilities. The authors identified NEA 2010 JL33 as the most likely object to be long-lost, and now inactive, Comet Lexell. 2010 JL33 is a dark (albedo of 0.047) object with a diameter of ~1.8 km which is consistent with a cometary nucleus. JL33’s next perihelion will occur in July 2019 at 0.71 AU. The object will be faint at 19th magnitude at that time and poorly placed at an elongation of 41 degrees.

A pre-print of the paper can be found at https://arxiv.org/pdf/1802.08904.pdf .

- Carl Hergenrother (ALPO Comet Section Coordinator)

ALPO COMET NEWS – JANUARY 2018

2018-January-1

Happy New Year! and Welcome to 2018. This year promises to be an exciting year for the Comet Section. New discovery C/2017 T1 (Heinze) is already bright enough for small telescope observers. Later in the year, the following comets should also become nice small telescope targets: 21P/Giacobini-Zinner (magnitude 6 in September), 38P/Stephen-Oterma (magnitude 9 in November), 46P/Wirtanen (magnitude 3 in December), 64P/Swift-Gehrels (magnitude 9 in October/November), C/2017 S3 (PANSTARRS) (magnitude 7 in August though it may get even brighter when too close to the Sun to be observable) and C/2017 T3 (ATLAS) (magnitude 8 in July/August). For large telescope and/or CCD observers, there are many dozens of comets that will become bright enough to observe this year.

Continuing our recent ALPO Comet News format, each release will concentrate on comets that are brighter than 12th magnitude. Fainter comets of interest may also be highlighted. This month four comets are expected to be brighter than 12th magnitude for part of the month: C/2017 T1 (Heinze), C/2016 R2 (PANSTARRS), 185P/Petriew and 62P/Tsuchinshan. At 13-14th magnitude, distant centaur comet 174P/Echeclus is once again in outburst.

Evening Comets

C/2017 T1 (Heinze) [Perihelion on 2018 February 21 at 0.58 au]

The new year kicks off with immediate action courtesy of comet C/2017 T1 (Heinze). As the month begins, you’ll have to battle the first Full Moon of January to see the comet. By the evening of the 2nd or 3rd, there should be enough dark time between the end of twilight and moonrise to grab a quick peak at Heinze. With a closest approach to Earth on January 4 at 0.22 au, the comet should brighten from magnitude 9.2 on the 1st to a peak of around 8.8 a week later. After that the comet will continue to approach the Sun (perihelion on February 21 at 0.58 au) but due to an increase in the comet-Earth distance (from the 0.22 au minimum to 0.79 au at the end of the month) the comet should experience a slow fade to magnitude 9.8 by February 1st.

Recent visual observations of Heinze from December 29 UT with 30×125 binoculars under a LM = 6.0 sky show it to be a rather diffuse (5′) low surface brightness object with little condensation or elongation. It is likely that observers under brighter skies and/or using high magnifications/large apertures will see the comet as much smaller and fainter.

Even with the bright Moon, CCD imagers may want to observe Heinze during the first few days of January. On January 3rd, the Earth passes through the comet’s orbit plane. As a result, the comet’s dust tail will be seen edge on. While dust tails seem to appear to be 3-dimensional tubes of material, in fact, they are usually 2-dimensional sheets. Similar to Saturn ring plane crossings, comet orbit plane crossings are when we are looking directly along the plane of the dust tail ’sheet’. On the days around orbit plane crossing, the dust tail will appear to narrow and may even grow in length as the surface brightness of the tail increases. CCD and large aperture visual observers will also notice the position angle of the tail rapidly swinging from the SSW on the 1st to nearly due east by the 10th.

Comet Heinze was discovered by Aren Heinze with the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey on October 2nd at 18th magnitude. The comet appears to be intrinsically faint. Based on the first few orbits from the MPC, it also appeared to be dynamically new. The latest orbit (released on December 31) make it more likely that Heinze is a dynamically old comet. While faint dynamically new comets have a tendency of not surviving their perihelion passage, faint dynamically old comets should be robust enough to survive. Regardless, all observers are asked to keep a close watch on Heinze as it nears perihelion and to look for any changes in coma morphology that might suggest a splitting or disintegration event.

Heinze will be moving rapidly through the northern evening sky this month. It starts the month in Lynx (Jan 1-3) before moving through Camelopardalis (3-6), Cassiopeia (6-12), Andromeda (12-13), Lacerta (14-22) and Pegasus (22-31). Northern observers should be able to follow Heinze into early February before it gets too close to the Sun. After that it will be too far south for northern observers. Heinze might be glimpsed from mid-latitude observers in the southern hemisphere during the first day or two of January. The comet will again become visible to southern observers in mid to late March about 1 month after perihelion. By then the comet will have faded to 11th magnitude or fainter.

The ephemeris below (and for all following comets) was produced with Seiichi Yoshida’s ‘Comet for Windows’ program with my best estimate of each comet’s photometric parameters. Comet brightness forecasts are prone to error due to sudden outbursts and changes in brightness trends so don’t be surprised if a comet’s brightness deviates from what is shown below. Also it is suggested that you use your favorite online ephemeris generator or planetarium program to determine exact positions for your time of observation.

The image below was taken by ALPO Comet Section contributor Charles Bell on December 29 with a 0.3-m Schmidt-Cassegrain + CCD + R band filter. It consists of 48 x 12 second exposures. Charles maintains a very active and informative Twitter account focused on comet news and observations. I highly recommend it.

C/2016 R2 (PANSTARRS) [Perihelion on 2018 May 9 at 2.60 au]

Comet C/2016 R2 (PANSTARRS) was a bit of a sleeper for much of 2016. A dynamically old long-period comet, it was expected to brighten rapidly as it approached perihelion. Instead the comet intrinsically faded during the first three quarters of 2017. Starting in October, it rapidly brightened from magnitude 14 to 10.7. While not the brightest comet, it has entertained CCD imagers with an intricate and rapidly changing ion tail reminiscent of comets C/1908 R1 (Morehouse) and C/1961 R1 (Humason). All three comets share one trait that may explain their unusual tails, they are all very rich in CO+.

The comet is still about 5 months out from its May 9 perihelion at a rather distance 2.60 au. This month its heliocentric distance will drop from 2.93 to 2.80 au. Any intrinsic brightening will be partially countered by an increasing geocentric distance (increasing from 2.07 to 2.29 au). As a result, the comet should only brighten from about magnitude 10.7 to 10.4 this month. It is very possible that the comet may even fade in apparent magnitude if its recent rapid increase in intrinsic brightness moderates. This month PANSTARRS is an evening object spending the entire month in Taurus.

185P/Petriew [Perihelion on 2018 Jan 27 at 0.93 au]

Jupiter-family comet 185P/Petriew was a visual discovery by Canadian amateur astronomer Vance Petriew with his 20″ dobsonian while star hopping to the Crab Nebula (M1) at the 2001 Saskatchewan Summer Star Party. 185P/Petriew is on an orbit with a period of 5.5 years and is making its 4th observed return this year. With a perihelion distance of 0.93 au, this comet has peaked between magnitude 9 and 12 at each return. This year it should peak at magnitude 11 around the time of perihelion (January 27) and closest approach to Earth (mid-February at 1.33 au) when located in the western evening sky. It is interesting that this comet was not discovered till 2001. Its perihelion was 1.0 au or less for three returns prior to discovery (1984, 1990, 1996). The 1990 return was comparable to this year’s and the 1984 return was much better. For nearly a 100 years before 1984, it perihelion was larger but not by too much (between 1.21 and 1.40 au).

For the current return, few observations of this comet have been reported to, or at least published by, the usual astrometric and photometric archives (MPC, COBS, ICQ, BAA, German Comet Group, ALPO). According to past behavior, 185P should be near magnitude 12.0 at the start of the month and brighten to near magnitude 11.0 by the end of January. Once the Moon leaves the evening sky, it will be interesting to see how bright 185P really is. On January 1, the comet will be located 1.01 au from the Sun and 1.52 au from Earth. These distances drop to 0.94 au from the Sun and 1.36 au from Earth at the end of the month. The comet can be observed moving against the stars of Capricornus (Jan 1-8), Aquarius (8-31) and Pisces (31).

174P/Echeclus [Perihelion on 2015 April 21 at 5.81 au]

Centaur comet 174P/(60558) Echeclus orbits the Sun on a 35 year orbit that carries it from just outside the orbit of Jupiter to between the orbits of Saturn and Uranus. While not quite as outburst prone as 29P/Schwassmann-Wachmann 1, Echeclus has experienced a number of multi-magnitude outbursts since 2006. Brian Skiff of Lowell Observatory discovered a new outburst of Echeclus on December 7. Over the following days and weeks the object brightened to magnitude 13.5 to 14.0. CCD observers continue to image a slowly expanding cloud of dust. The cloud is expected to continue to expand and slowly fade this month. Echeclus is currently an evening object and can be found in Aries (Jan 1-31).

I was able to remotely image 174P on December 24 with a 0.51-m telescope located at Warrumbungle, Australia. The telescope is part of the Sierra Star Observatory Network.

Morning Comets

62P/Tsuchinshan [Perihelion on 2017 Nov 16 at 1.38 au]

Discovered photographically in 1965, 62P/Tsuchinshan (Chinese for Purple Mountain which is the name of the observatory where the discovery was made) is making its 9th observed return. The comet was observed between magnitude 10.5 and 11.5 from late October into December. This month, its heliocentric distance increases from 1.48 to 1.62 au while its geocentric distance drops from 1.20 to 1.11 au as it moves through Virgo (Jan 1-31) in the morning sky. The comet should fade by nearly a magnitude over the course of the month from around 11.1 to 11.9.

- Carl Hergenrother (ALPO Comet Section Coordinator)

ALPO COMET NEWS – DECEMBER 2017

2017-December-6

The Geminid meteor shower is always a highlight for planetary observers in December. This month also provides a nice opportunity to observe the largest “Geminid” of all, asteroid 3200 Phaethon. The Geminid parent body will brighten to magnitude 10.7 as it passes within 0.07 au of Earth. Another object, 2017 VT14, that could be cometary based on its orbit, may make a historic close approach to within 0.01 au of Earth though it may be too faint except for CCD imagers. As for active comets, C/2017 T1 (Heinze) will be interesting to watch as it approaches perihelion early next year. This intrinsically faint, dynamically new comet may brighten to 9-10th magnitude this month.

Evening Comets

29P/Schwassmann-Wachmann 1 [Perihelion on 2019 March 7 at 5.77 au]

The 2017 season for observing 29P is drawing to a close as the comet is slowly sinking lower in the wester sky after dusk. The comet continues its elevated activity level and is currently 13th magnitude. CCD imagers are asked to keep monitoring it as long as possible before it is lost till after solar conjunction. 29P is located near the border of Aquarius and Capricornus.

C/2017 O1 (ASASSN) [Perihelion on 2017 Oct 13 at 1.50 au]

The brightest comet of the past few months (that didn’t require a spacecraft to observe) was C/2017 O1 (ASASSN). After obtaining a peak brightness of magnitude 8-9 in September and October, the comet started to fade in November. As seems to be typical for large diffuse comets, there is quite a bit of scatter in the current magnitude estimates with most observers placing it around magnitudes 10 and 11. The comet should continue to fade as it moves away from the Sun (1.64 on Dec 1 to 1.84 au on Jan 1) and Earth (0.95 to 1.23 au). For those wanting to take a look at ASASSN, it will be located in the northern circumpolar sky as it moves through the Milky Way constellation Cepheus this month.

3200 Phaethon [Perihelion on 2017 January 25 at 0.14 au]

Asteroid 3200 Phaethon is the parent body of the Geminid meteor shower. Whether the shower was produced by long-lasting cometary activity or a series of splitting events, the Geminids are now one of the strongest annual showers. Recently Phaethon has been observed to display comet-like activity around perihelion. Due to intense heating (perihelion is 0.14 AU from the Sun or 7 times closer than Earth) some of the rocks on the surface may have fractured producing a cloud of dust which was knocked off the surface by solar radiation pressure. In effect, it is a acting like a “rock comet”. Still these sort of events are very short-lived and produce minimal amounts of debris, hence they are not large enough to create the large mass of existing Geminids by themselves.

This year Phaethon will pass 0.069 au from Earth on December 16 and brighten to magnitude 10.7. While little to no cometary activity is expected, such a close approach does provide an opportunity to directly study the surface of Phaethon via time-resolved and color photometry. Lightcurve, color and phase function photometry are requested for better understanding of this enigmatic object which is now also the target of a proposed Japanese-lead spacecraft mission, Destiny+ (see presentations on Destiny+ here and here). With a rotation period of 3.6 hours, an entire rotation can be observed during a relatively short observing session. This is the closest approach to Earth by Phaethon since 1974 (0.055 au) and till 2093 (0.020 au). Phaethon starts the month 1.25 au from Sun, 0.31 au from Earth and V magnitude 13.7. It rapidly moves across the evening sky constellations of Auriga (Dec 1-11), Perseus (11-14), Andromeda (14-17), Pegasus (17-19), Aquarius (19-21) and Capricornus (21-31) before ending the month at 0.73 au from Sun and 0.29 au from Earth.

2017 VT14 [Perihelion on 2017 Dec 11 at 0.98 au]

Phaethon won’t be the only “is it a comet or asteroid” object passing close to Earth this month. Though its orbit suggests no relationship to Phaethon, 2017 VT14 will pass close to Earth only hours after Phaethon.

2017 VT14 was discovered on November 13 by the NEOWISE satellite in low Earth orbit. As of November 23, when it was last observed, this object has not shown any cometary activity. Its orbit is similar to a Jupiter family comet and backwards integration of the orbit uncovers a number of recent close approaches to Jupiter. VT14 will pass 0.0098 au from the Earth on December 17. If it is recognized as a comet, it may make the closest cometary approach in recorded history. Comet D/1770 L1 (Lexell) passed within 0.0151 au of Earth in 1770. Only one other comet may have come closer though it is based on a very poorly determined orbit (C/1491 B1 at 0.0094 au).

VT14 starts the month at 0.99 au from Sun and 0.10 au from Earth. Perihelion occurs on December 11 at 0.98 au. By the end of the month, VT14 will be located 1.02 au from Sun and 0.09 au from Earth. If it remains inactive, it will start the month at V magnitude 20.5, peak at 16.0 on December 17 and end the month at 19.6. If it becomes active, it could be many magnitudes brighter.

The object will quickly move through the following constellations: Pegasus (Dec 1-12), Aquarius (12-15), Sculptor (15-16), Phoenix (16), Tucana (16-17), Hydrus (17, Horologium (17), Dorado (17-18), Volans (18), Carina (18-19), Vela (19-21), Pyxis (21-22), Antlia (22-31), and Hydra (31). It will be lost to most northern hemisphere observers just hours to days before closest approach. CCD observers are encouraged to closely watch this object for any sign of cometary activity. Similar to Phaethon, this is also a great opportunity to acquire lightcurve, color and phase function photometry for this object.

Morning Comets

24P/Schaumasse [Perihelion on 2017 Nov 16 at 1.21 au]

Short-period comet 24P/Schaumasse is making its 11th observed return since its discovery back in 1911 by French astronomer Alexandre Schaumasse. Perihelion occurred last month on November 16 at 1.21 au and closest approach to Earth on November 21 at 1.46 au. On November 26, I saw 24P with my C14 at 98x at magnitude 11.2. It was small (2.5′) with a diffuse coma and no sign of a tail. This month, comet Schaumasse should slowly fade from magnitude 11 to 12 as it moves through Leo (Nov 1-8) and Virgo (8-30). Now past its November 16 perihelion, Schaumasse will recede from the Sun (1.22 to 1.34 au) and Earth (1.46 t o 1.50 au) this month.

62P/Tsuchinshan [Perihelion on 2017 Nov 16 at 1.38 au]

Discovered photographically in 1965, 62P/Tsuchinshan (Chinese for Purple Mountain which is the name of the observatory where the discovery was made) is making its 9th observed return. The comet was observed between magnitude 10.5 and 11.0 for much of late October into November. On November 26, I observed 62P with my C14 at 98x at magnitude 10.8. Similar to 24P, 62P was small (2′) with a diffuse coma and no sign of a tail. This month, its heliocentric distance increases from 1.39 to 1.47 au while its geocentric distance drops from 1.29 to 1.20 au as it moves through Leo (Nov 1-26) and Virgo (26-30) in the morning sky.

C/2017 T1 (Heinze) [Perihelion on 2018 February 21 at 0.58 au]

C/2017 T1 (Heinze) is a recent discovery by Ari Heinze with the ATLAS (Asteroid Terrestrial-impact Last Alert System) survey on October 2nd at 18th magnitude. Perihelion will be on February 21 at 0.58 au. The comet appears to be intrinsically faint but due to a small perihelion distance and a pre-perihelion close approach to Earth in early January at 0.22 au, it is possible that this comet may brighten to magnitude 9.5 to 10.0 by the end of this month. If Heinze is going to get that bright, it better get a move on. While we haven’t received any observations of Heinze in November, recent observations submitted to COBS show the comet had only brightened to 15th magnitude by the end of November.

This will be an interesting comet to watch this month. A dynamically new and intrinsically faint comet, Heinze may not survive its perihelion passage. CCD imagers (and if it brightens further, visual observers) should keep this comet under close watch. Heinze starts the month at 1.70 au from the Sun and 1.08 au from Earth. By the end of the month, the comet is much closer to the Sun (1.21 au) and Earth (0.25 au). It moves through Hydra (Dec 1-17) and Cancer (17-31) this month.

C/2016 R2 (PANSTARRS) [Perihelion on 2018 May 9 at 2.60 au]

C/2016 R2 (PANSTARRS) reaches perihelion in May at 2.60 au from the Sun. For much of 2017, C/2016 R2 showed little increase in activity. That all changed last month as the comet brightened from 14th to 11th magnitude. This month, PANSTARRS should continue to brighten as its perihelion distance drops from 3.09 to 2.94 au and it geocentric distance drops from 2.14 to 2.05 au before increasing back to 2.07 au. The comet passes though opposition this month as it moves against the stars of Orion (Dec 1-16) and Taurus (16-31).

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

- Carl Hergenrother (ALPO Comet Section Coordinator)

ALPO COMET NEWS – NOVEMBER 2017

2017-November-5

The brightest comet of the month will probably not be observed directly by anyone from Earth as 96P/Machholz will remain too close to the Sun after its October perihelion. The brightest nighttime comet should be C/2017 O1 (ASASSN) as it fades from 9th to 10th magnitude. The second and third brightest nighttime comets should be returning periodic comets 24P/Schaumasse and 62P/Tsuchinshan. While 24P is predicted to be brighter (at magnitude 10.5 vs 11.5), observations during October suggest that 62P may be the one that brightens to magnitude 10.5 with 24P being fainter.

Evening Comets

29P/Schwassmann-Wachmann 1 [Perihelion on 2019 March 7 at 5.77 au]

Outburst prone 29P/Schwassmann-Wachmann has been quite active this year. The comet has been consistently observed between magnitude 11 and 14 since September. How bright it will be this month depends on whether it experiences another outburst. This is one comet where rapid changes in brightness and coma morphology make day-to-day (and sometimes even hour-to-hour) monitoring worthwhile. CCD imagers are especially asked to keep a watch on this enigmatic object as it slowly drifts near the Capricornus/Aquarius border in the evening sky.

C/2017 O1 (ASASSN) [Perihelion on 2017 Oct 13 at 1.50 au]

As November starts, the brightest comet in the night sky is C/2017 O1 (ASASSN). Due to this comet’s diffuse and large coma, a large range of magnitude estimates has been reported. Binocular observers have reported the comet to be between magnitude 8.5 and 9.0 while larger telescope observers have reported the comet to be as faint as magnitude 10.5. In my 30×125 binoculars, ASASSN is large (7-8′), very diffuse and hard to detect as anything more than a faint brightening against the background sky. It could be easy to miss under a Moon-lit or light polluted sky. This month the comet should fade as it is moving away from the Sun (1.52 to 1.64 au) and Earth (0.75 to 0.95 au). For those willing to take a look at ASASSN, it will be located in the northern circumpolar sky as it moves through Camelopardalis (1-15) and Cepheus (15-30).

Morning Comets

24P/Schaumasse [Perihelion on 2017 Nov 16 at 1.21 au]

Short-period comet 24P/Schaumasse is making its 11th observed return since its discovery back in 1911 by French astronomer Alexandre Schaumasse. Perihelion occurs this month on November 16 at 1.21 au and closest approach to Earth on the 21st at 1.46 au. The comet was expected to peak at 10-11th magnitude this month. Recent visual observations show it to be running 1-2 magnitudes fainter than predicted. At the end of October, the comet was between 12-13th magnitude. Whether it brightens to 10th magnitude remains to be seen but it is very possible that Schaumasse may not get brighter than 11-12th magnitude. this month as it moves through Leo (Nov 1-8) and Virgo (8-30). Its next return in late 2025/early 2026 will be better with a close approach to Earth of 0.59 au.

62P/Tsuchinshan [Perihelion on 2017 Nov 16 at 1.38 au]

While 24P/Schmaumasse underperforms, 62P/Tsuchinshan appears to be a brighter than expected. Discovered photographically in 1965, 62P/Tsuchinshan (Chinese for Purple Mountain which is the name of the observatory where the discovery was made) is making its 9th observed return. The comet was observed between magnitude 10.5 and 11.0 at the end of October. It should brighten by another 0.5 to 1.0 magnitude as it reaches perihelion on Nov 16 at 1.38 au. This brightness would match 62P’s performance at its return in 1985. Looking ahead, its next return in late 2023/early 2024 will be even better with a lower perihelion distance (1.26 in 2023 vs 1.38 au this year) and geocentric distance (0.50 au in 2023). This month, its heliocentric distance stays around 1.38 au and its geocentric distance drops from 1.41 to 1.29 au as it moves through Leo (Nov 1-26) and Virgo (26-30) in the morning sky.

New Discovery

The last Comet Section post introduced two recent discoveries that should become bright enough for visual observers, C/2017 T1 (Heinze) and C/2017 T2 (PANSTARRS). The ATLAS survey, which also discovered C/2017 T1, has found another comet which should become bright in 2018. C/2017 T3 (ATLAS) was discovered on October 14 at 18th magnitude. The comet is currently in the far northern sky in Cepheus at a distance of 3.8 au from the Sun. It comes to perihelion on 2018 July 19 at 0.83 au. Unfortunately, it does not get too close to Earth (1.35 au on August 1) though it is possible that this dynamically old long-period comet will brighten to magnitude 9 or 10 around perihelion.

Mike Olason imaged two of the recent discoveries (C/2017 T1 and C/2017 T2) with his 11″ SCT and SBIG STF-8300M CCD from Colorado.

- Carl Hergenrother (ALPO Comet Section Coordinator)

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