ALPO COMET NEWS FOR NOVEMBER 2018
2018-November-5
Comet 46P/Wirtanen rapidly brightens this month as it approaches to within 0.078 AU of the Earth on Dec 16. Depending on how dark your skies are, Wirtanen may be a naked eye object in December (or even as early as late November). Wirtanen isn’t the only cometary attraction this month. Two short-period comets come to perihelion in November. Both 38P/Stephan-Oterma and 64P/Swift-Gehrels should peak between magnitude 9 and 9.5 this month.
Bright Comets (magnitude < 10)
38P/Stephan-Oterma – Halley family comet 38P/Stephan-Oterma has an orbital period of ~38 years and is returning for the first time since 1980. This comet has a bit of an interesting backstory. In 1867, it was first sighted by Jérôme E. Coggia (Marseilles, France) who thought he had found an uncatalogued nebula. Over the following nights, followup observations by E. J. M. Stephan (Marseilles, France) uncovered the true nature of the object. For some reason, the discovery announcement cited Stephan as the discoverer with no mention of Coggia. After being missed at its next return in 1904, the comet was photographically rediscovered in 1942 by Liisi Oterma (Turku, Finland).
Stephen-Oterma is a morning object though it should be high enough to observe for most northern observers by 11 pm to midnight. This month should see the comet at its brightest (between magnitude 9.0 and 9.5) as it reaches perihelion (1.59 AU) on November 10 and closest approach to Earth (0.77 AU) on December 17. It will be moving through Gemini (Nov 1-25, 28-29) and Cancer (25-28, 29-30).
38P/Stephan-Oterma T = 2018-Nov-10 q = 1.59 AU Short-Period comet Period = 38.0 yr Date Mag R.A. Decl. r d Elong const 2018-11-01 9.6 07 10 +18 37 1.593 0.935 111 Gem 2018-11-11 9.4 07 32 +21 30 1.588 0.872 116 Gem 2018-11-21 9.3 07 52 +24 50 1.593 0.823 122 Gem 2018-12-01 9.3 08 09 +28 34 1.608 0.788 129 Cnc
46P/Wirtanen – The brightest comet of the year will be 46P/Wirtanen which passes within 0.078 AU of the Earth in mid-December.
While the comet is still a southern object, this month sees the comet start its acceleration northward across the sky. Starting the month at a declination of -33 degrees, Wirtanen ends the month at -19 degrees as it moves through Fornax (Nov 1-27) and Cetus (27-30). Next month the comet will be located at significantly more northern declinations.
Chris Wyatt reported Wirtanen to be at magnitude 7.7 on November 3. This is very close to the prediction based on past apparitions. Its rapid brightening should bring the comet to magnitude 7.0 by the 10th, 6.0 by the 20th and 5.0 by the 28th. Recent CCD images by Martin Mobberley have even caught the development of a gas tail.
Assuming it behaves as in the past, Wirtanen should peak around magnitude 3 in mid-December. Note, that as a short-period comet, Wirtanen is likely to be a large diffuse object around the time of closest approach. It is possible its coma diameter will be in excess of 1 degree. Already visual observations by Chris Wyatt and CCD observations by Raymond Ramlow show Wirtanen to possess a coma with a diameter of 20+ arc minutes (0.33 degrees). Even at its brightest, do not expect the comet to appear as bright as a 3rd magnitude star since its light will be spread over a large area. Observers may need a relatively dark sky to see Wirtanen with the naked eye.
46P/Wirtanen
T = 2018-Dec-12 q = 1.06 AU Short-Period comet Period = 5.4 yr
Date Mag R.A. Decl. r d Elong const
2018-11-01 8.0 01 59 -33 03 1.195 0.275 132 For
2018-11-11 6.9 02 02 -32 33 1.140 0.221 128 For
2018-11-21 5.8 02 11 -29 05 1.096 0.169 126 For
2018-12-01 4.6 02 32 -19 51 1.068 0.121 129 Cet
64P/Swift-Gehrels – Comet Swift-Gehrels was originally discovered visually by Lewis Swift (Rochester, New York) in 1889. Swift was also the discoverer of the Perseid parent body, Swift-Tuttle. After the 1889 apparition Swift’s comet went unobserverd until 1973 when its was rediscovered by Tom Gehrels on photographic plates taken at Palomar Observatory in southern California. 2018 marks Swift-Gehrels’ 7th observed return. Since its discovery in 1889, the comet’s orbit has been fairly stable with an orbital period of 9.4 years and perihelion distance near its current value of 1.39 AU. Not an especially bright object, this year’s return will be its best known return with a minimum Earth-comet distance of 0.44 AU on October 28. You will have to wait till 2092 for another return as good as this year’s though the 2046 return will be just a little worse than this year.
64P has already shown some excitement with a short lived outburst that saw it brighten by ~2-3 magnitudes to around 13th magnitude in mid-August. After its outburst, Swift-Gehrels seemed to be running a little brighter than expected. The most recent magnitude estimates from Chris Wyatt and Salvador Aguirre place the comet around magnitude 9.9-10.0 which is fairly close to its predicted brightness.
Now an evening object, Swift-Gehrels can be seen moving through Andromeda (Nov 1-25) and Triangulum (25-30). Perihelion occurs on November 3 at 1.39 AU and closest approach to Earth was a week earlier on October 27 at 0.44 AU. In the past, the comet reached its peak intrinsic brightness five weeks after perihelion. If it follows the same pattern, Swift-Gehrels should continue to brighten to a late November peak at magnitude 9.5.
64P/Swift-Gehrels
T = 2018-Nov-03 q = 1.39 AU Short-Period comet Period = 8.9 yr.
Date Mag R.A. Decl. r d Elong const
2018-11-01 10.1 00 48 +36 53 1.394 0.446 148 And
2018-11-11 9.7 01 02 +36 45 1.396 0.457 146 Tri
2018-11-21 9.5 01 20 +35 54 1.408 0.481 144 Tri
2018-12-01 9.5 01 42 +34 34 1.431 0.519 141 Tri
Faint Comets (between magnitude 10 and 13)
21P/Giacobini-ZInner - Short-period comet 21P/Giacobini-Zinner is now two months past its September perihelion. After reaching a peak brightness of around magnitude 7.0, the comet faded more rapidly than expected in October. A CCD observation by Raymond Ramlow on November 4 found Giacobini-Zinner at magnitude 10.4.
November should see the comet steadily fade as it moves away from the Sun and Earth. The comet also continues moving deeper into the southern sky. Visual and CCD observers can continue to enjoy the comet moving against the rich Milky Way constellations of Canis Major (Nov 1-11) and Puppis (11-30).
Looking ahead, Giacobini-Zinner’s next return in 2025 will be very poor with the comet located on the other side of the Sun at perihelion. In 2031 the comet will be better placed with a minimum Earth-comet distance of 0.55 AU (versus 0.39 AU this year) and a slightly larger perihelion distance of 1.07 AU (versus 1.01 AU this year). The comet should brighten to magnitude 8 or so that year.
21P/Giacobini-Zinner T = 2018-Sep-10 q = 1.01 AU Short-Period comet Period = 6.5 yr Date Mag R.A. Decl. r d Elong const 2018-11-01 10.4 07 25 -28 08 1.245 0.660 95 CMa 2018-11-11 11.2 07 24 -33 09 1.326 0.727 99 CMa 2018-11-21 11.9 07 17 -36 42 1.412 0.793 104 Pup 2018-12-01 12.5 07 07 -38 53 1.501 0.859 108 Pup
C/2016 M1 (PANSTARRS) – Comet C/2006 M1 (PANSTARRS) continues to slowly fade. Visual observations by Chris Wyatt on November 3 found the comet at magnitude 10.4. Having passed perihelion on August 10 at 2.21 AU and now moving away from both the Earth and Sun, C/2016 M1 should continue to slowly fade as it moves through the southern constellations of Circinus and Apus.
C/2016 M1 (PANSTARRS)
T = 2018-Aug-10 q = 2.21 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-11-01 10.7 14 50 -68 16 2.406 2.848 54 Cir
2018-11-11 10.9 15 03 -70 56 2.453 2.906 53 Aps
2018-11-21 11.0 15 20 -73 52 2.504 2.950 54 Aps
2018-12-01 11.2 15 42 -77 04 2.558 2.982 55 Aps
C/2016 N6 (PANSTARRS) – Yet another faint, high q, PANSTARRS discovery, C/2016 N6 was imaged by Raymond Ramlow at magnitude 12.6 on November 2nd and observed visually by J. J. Gonzalez at magnitude 11.8 on October 20. The comet is now 4 months past perihelion (2.67 AU on July 18, 2018). A decreasing Earth-comet distance will result in the comet staying near magnitude 12 even though it is moving away from the Sun in November.
C/2016 N6 (PANSTARRS)
T = 2018-Jul-18 q = 2.67 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-11-01 12.2 08 54 +02 17 2.889 2.836 83 Hya
2018-11-11 12.2 08 47 -01 09 2.930 2.699 93 Hya
2018-11-21 12.2 08 37 -04 44 2.974 2.575 104 Hya
2018-12-01 12.2 08 23 -08 28 3.020 2.473 114 Hya
Other Comets of Interest
(944) Hidalgo and (3552) Don Quixote – Two bright low activity or dormant comets come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though a tail was seen in 2009 with the Spitzer IR space telescope and again this March at visible wavelengths with a 4.1-m telescope. This month Don Quixote is fading from magnitude 16.5 to 17.2. (944) Hidalgo reaches peak brightness at magnitude 14.3 this month. Unlike Don Quixote, Hidalgo has shown no cometary activity so far.
(944) Hidalgo
T = 2018-Oct-26 q = 1.95 AU Extinct comet Period = 13.8 yr
Date Mag R.A. Decl. r d Elong const
2018-11-01 14.4 08 35 +70 59 1.948 1.476 102 UMa
2018-11-11 14.3 09 34 +73 38 1.954 1.456 104 Dra
2018-11-21 14.3 10 37 +75 27 1.964 1.448 105 Dra
2018-12-01 14.3 11 36 +76 34 1.979 1.450 107 Dra
(3552) Don Quixote
T = 2018-May-07 q = 1.24 AU Extinct comet Period = 8.8 yr
Date Mag R.A. Decl. r d Elong const
2018-11-01 16.5 01 29 +54 13 2.393 1.556 138 Cas
2018-11-11 16.7 01 12 +53 05 2.475 1.647 138 Cas
2018-11-21 16.9 01 01 +51 31 2.557 1.759 135 Cas
2018-12-01 17.2 00 56 +49 49 2.638 1.891 130 Cas
As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)
