ALPO COMET NEWS FOR JULY 2018
2018-July-1
Hello Comet Observers!
This month we may see as many as 4 comets become brighter than 9th magnitude. Two are located at far northern declinations while the other two will only be visible to far southern observers.
Bright Comets (magnitude < 10)
C/2016 M1 (PANSTARRS) – The brightest comet of the past two months was well observed in June as it moved southwestward through Sagittarius and Ara. It was fun to watch it glide through such a globular rich part of the sky. By the end of June visual observers were estimating the comet to be between magnitude 7.7 and 8.7. CCD observations by Raymond Ramlow found a brightness that was closer to the brighter end of the visual range. Visual coma diameters ranged from 4′ to 8′ during the last week of June with CCD coma diameters as large as 13′.
The comet is now located at a declination of -46 degrees, putting it out of range for most northern mid-latitude observers. For southern observers it will be located nearly overhead during the late evening. The comet will start the month near peak brightness but should slowly fade as the month progresses. Although perihelion isn’t till August 10, the fading is due to the comet is currently moving away from Earth.
C/2016 M1 (PANSTARRS)
T = 2018-Aug-10 q = 2.21 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-07-01 8.3 17 39 -46 24 2.259 1.301 153E Ara
2018-07-11 8.4 16 51 -51 31 2.238 1.368 139E Ara
2018-07-21 8.5 16 05 -54 33 2.223 1.482 124E Nor
2018-07-31 8.6 15 28 -56 06 2.214 1.625 111E Cir
C/2017 S3 (PANSTARRS) – This comet is the biggest question mark of the month as it approaches perihelion on August 15 at the small distance of 0.21 AU from the Sun. Its orbit suggests that S3 is a dynamically new comet making its first trip through the inner solar system. Dynamically new comets have a tendency to appear very bright when far from the Sun. The enhanced brightness may be due to extremely volatile ices sublimating at low temperatures when far from the Sun. Analysis of the dust tail of dynamically new and now defunct C/2012 S1 (ISON) found evidence of dust released at distances as great as 100 AU! (Sekanina and Kracht, 2014)
Since discovery S3 has shown little intrinsic brightening. That is until late June. Recent CCD images by Raymond Ramlow found the comet to be magnitude 12.3 on June 26. This is ~2 magnitudes brighter than predicted in last month’s ALPO Comet News. That prediction did come with the caveat that gas-rich comets may brighten at a faster rate as they get closer to the Sun. Whether the current brightness increase is due to the development of a larger gas coma is supported by an increase in CCD detected coma diameter from <1′ to 2.2-2.3′.
Of course the question every one wants answered is how bright will S3 get. Well… it is probably too early to tell. There is not enough data to determine whether the 2 magnitude jump was a sudden event or the start of a new brightening trend. For now the magnitudes below may be very off. I’ll update them as more data comes in. An old saying about forecasting the stock market also applies to comets. “If you’re going to predict, predict often.”
S3 is only a northern hemisphere object as it is located close to and north of the Sun. It is circumpolar for much of the month though it is easier to observe in the morning. All observers are asked to observe this object as often as possible. Not only to watch its brightness trend but also to watch for signs of disintegration. Even after the 2 magnitude bump, dynamically new comets as faint as S3 have a high probability of disintegration as they near the Sun.
C/2017 S3 (PANSTARRS)
T = 2018-Aug-15 q = 0.21 AU Long-Period comet - dynamically new
Date Mag R.A. Decl. r d Elong const
2018-07-01 11.8 03 01 +59 24 1.237 1.562 52M Cas
2018-07-11 10.7 03 59 +58 25 1.030 1.308 50M Cam
2018-07-21 9.1 05 14 +54 18 0.807 1.051 45M Aur
2018-07-31 7.0 06 47 +42 05 0.562 0.827 33M Aur
C/2017 T3 (ATLAS) - Out of view since April, Comet ATLAS was picked up again visually by Chris Wyatt. He observed the comet to be magnitude 9.4 on June 22nd and 8.8 on the 23rd. Ever since its discovery by the Hawai’i-based ATLAS (Asteroid Terrestrial-impact Last Alert System) project in October of last year, ATLAS has been brightening at a slightly faster than expected rate. The new observations show that it continues to brighten at a slightly faster than normal rate (2.5n ~ 12 compared to 2.5n ~ 10 which is usually, and often incorrectly, assumed for all long-period comets). The rapid brightening is not atypical for a dynamically old comet (one that has been through the inner solar system before).
Perihelion occurs this month on the 19th at 0.83 AU though the comet will be a rather distant 1.4 AU from the Earth at that time. Peak brightness occurs towards the end of this month at between magnitude 8.0 and 8.5. For southern hemisphere observers, the comet will be visible at a low elevations (~10 – 15 degrees). Unfortunately, it will be unobservable for northern hemisphere observers till the very end of the year when it will be a faint object (~16th magnitude).
C/2017 T3 (ATLAS)
T = 2018-Jul-19 q = 0.83 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-07-01 9.0 05 18 +05 24 0.893 1.685 26M Ori
2018-07-11 8.5 06 00 -02 11 0.840 1.526 31M Ori
2018-07-21 8.3 06 53 -10 51 0.826 1.406 35M Mon
2018-07-31 8.3 07 57 -19 23 0.855 1.352 39M Pup
21P/Giacobini-ZInner – Many long-time observers may remember this comet’s last excellent return in the fall of 1985 just as Comet Halley was approaching its 1986 perihelion. This year marks G-Z’s 16th observed return since its visual discovery in 1900 by Michel Giacobini (Nice, France). The comet was visually re-discovered 2 returns later in 1913 by Ernst Zinner (Bamberg, Germany), hence the double appellation. Perihelion and closest approach to Earth both occur on September 10 at 1.01 AU and 0.39 AU, respectively. This will be the comet’s closest approach to Earth since 1959 when it passed 0.35 AU from Earth.
Recent observations show that 21P has brightened to magnitude 11.0 to 12.0 by the last week in June. This month the comet is high in the morning sky (for northern observers) as it moves through Cygnus, Cepheus and Cassiopeia. It should rapidly brighten from around magnitude 11 to 10 by the midde of the month and 9 by the end of the month. Its current brightening is still consistent with a peak brightness of around magnitude 7 in early September. Though the comet will be located at high northern declinations over the next few months, it will travel far enough south for most southern hemisphere observers by mid-September.
21P/Giacobini-Zinner
T = 2018-Sep-10 q = 1.01 AU Short-Period comet Period = 6.5 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 11.1 21 28 +50 08 1.409 0.849 97M Cyg
2018-07-11 10.4 21 58 +55 48 1.323 0.762 95M Cep
2018-07-21 9.6 22 42 +61 05 1.242 0.679 92M Cep
2018-07-31 8.9 23 50 +65 14 1.169 0.600 88M Cas
Faint Comets (between magnitude 10 and 13)
37P/Forbes - A new comet to the ALPO Comet News, short-period comet Forbes was discovered by South African astronomer Alexander F. I. Forbes on August 1, 1929. 2018 marks the comet’s 15th apparition and 12th observed apparition since discovery. During its last return the comet experienced a 4 magnitude outburst some 9 months after perihelion. This year 37P was not expected to become brighter than ~13th magnitude. Recent observations place the comet anywhere from magnitude 10.3 to 13.6 over the past few weeks. Estimates of coma diameter are also all over the place (from 1′ to 9′) suggesting the comet’s perceived brightness may depend on how much of a low surface brightness coma is being detected by each observer. The magnitudes forecast below are splitting the difference between the late June observations.
37P/Forbes
T = 2018-May-04 q = 1.61 AU Short-Period comet Period = 6.4 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 12.0 23 31 -02 13 1.708 1.117 106M Psc
2018-07-11 12.1 23 39 +00 07 1.742 1.072 112M Psc
2018-07-21 12.2 23 44 +02 11 1.780 1.033 120M Psc
2018-07-31 12.3 23 45 +03 54 1.822 1.002 129M Psc
48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. The comet should brighten from around magnitude 13 to 12 this month as it moves among the stars of Capricornus in the morning sky. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.
Most observers have been consistently placing this comet around magnitude 14.0 which is ~2 magnitudes fainter than expected based on it previous returns. The only dissenter being J. J. Gonzalez who estimates it at the much brighter magnitude of 11.5. J. J. also is seeing a much larger coma so, again, there is some question as to whether a very low surface brightness extended coma is being missed by some observers.
48P/Johnson
T = 2018-Aug-12 q = 2.00 AU Short-Period comet Period = 6.5 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 11.9 22 28 -16 26 2.032 1.263 125M Aqr
2018-07-11 11.6 22 36 -17 38 2.021 1.180 133M Aqr
2018-07-21 11.4 22 41 -19 14 2.012 1.111 142M Aqr
2018-07-31 11.3 22 43 -21 08 2.007 1.059 150M Aqr
66P/du Toit – This marks 66P’s 4th observed and best apparition since its discovery by South African astronomer Daniel du Toit in 1944. Late June observations place the comet between magnitude 11.0 and 11.5. Now that 66P is past its May 19 perihelion, it should start to fade and this may be the last month to catch it visually. A difficult object for northern observers, 66P finally comes into view for those of us at mid-northern latitudes. The next return won’t be till 2033 though with a minimum comet-Earth distance of 1.36 AU it should be a fainter object at that return.
66P/du Toit
T = 2018-May-19 q = 1.29 AU Short-Period comet Period = 14.9 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 12.4 01 03 -22 15 1.410 0.923 93M Cet
2018-07-11 13.2 01 16 -20 04 1.467 0.924 98M Cet
2018-07-21 14.1 01 24 -18 15 1.532 0.922 104M Cet
2018-07-31 15.0 01 26 -16 47 1.604 0.918 111M Cet
364P/PANSTARRS – 364P/PANSTARRS is an example of a low activity comet. Similar to other comets of this type (such as 162P/Siding Spring, 169P/NEAT, 209P/LINEAR, 249P/LINEAR and 300P/Catalina), 364P is only active at small heliocentric distances. There is even some research that suggests that some of these objects originated in the Main Belt rather than the Kuiper Belt like most short-period comets.
Discovered in 2013 as P/2013 CU129, 364P is making its second observed return. This comet has a rather short period (4.9 years) and is only active for a few months around perihelion. Perihelion occurred last month on the 24th at 0.80 AU from the Sun. Peak brightness will occur a few weeks later closer to the time of closest approach to Earth on July 18 at 0.24 AU. The comet displayed a thin tail in May and June with a hint of a gas coma. Northern observers will be out of luck till early September while southern observers will have an uninterrupted view of the comet (though it will be very low in early July).
364P/PANSTARRS
T = 2018-Jun-24 q = 0.80 AU Short-Period comet Period = 4.9 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 10.9 08 18 -04 58 0.805 0.290 37E Hya
2018-07-11 10.8 07 23 -17 33 0.842 0.246 39E CMa
2018-07-21 11.4 06 04 -28 09 0.906 0.236 56M Col
2018-07-31 12.4 04 42 -33 38 0.988 0.253 76M Cae
C/2016 R2 (PANSTARRS) – C/2016 R2 passes through solar conjunction this month. Unless C/2016 N6 which will be too close to the Sun to be seen this month, C/2016 R2 will pass sufficiently far enough north of the Sun that it will always remain visible. During the June, the comet was observed between 11 and 12th magnitude. With a distant perihelion on May 2 at 2.60 AU, the comet should slowly fade.
C/2016 R2 (PANSTARRS)
T = 2018-May-02 q = 2.60 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-07-01 11.2 07 44 +51 51 2.661 3.476 31E Lyn
2018-07-11 11.3 08 14 +52 25 2.685 3.493 32E Lyn
2018-07-21 11.4 08 45 +52 41 2.713 3.504 33M UMa
2018-07-31 11.4 09 17 +52 39 2.745 3.513 35M UMa
Other Comets of Interest
Two low activity comet come to perihelion this year. (3552) Don Quixote is still designated an asteroid even though Spitzer Space Telescope observations from 2009 showed a faint coma and tail. This month Don Quixote is slowly fading from its peak brightness. (944) Hidalgo is still inbound and will peak in brightness at 14.3 in November. Unlike Don Quixote, Hidalgo has shown no cometary activity so far. Both objects are located close to each other in the morning sky.
(944) Hidalgo
T = 2018-Oct-26 q = 1.95 AU Extinct comet Period = 13.8 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 15.8 02 54 +20 49 2.263 2.749 51M Ari
2018-07-11 15.7 03 11 +24 09 2.216 2.606 56M Ari
2018-07-21 15.5 03 28 +27 40 2.172 2.463 61M Ari
2018-07-31 15.4 03 46 +31 22 2.131 2.322 66M Per
(3552) Don Quixote
T = 2018-May-07 q = 1.24 AU Short-Period comet Period = 8.8 yr
Date Mag R.A. Decl. r d Elong const
2018-07-01 16.0 02 01 +13 44 1.422 1.493 65M Ari
2018-07-11 16.1 02 17 +18 53 1.485 1.482 70M Ari
2018-07-21 16.2 02 31 +23 50 1.555 1.468 75M Ari
2018-07-31 16.2 02 43 +28 35 1.629 1.452 80M Ari
As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)
