ALPO COMET NEWS FOR JUNE 2018
2018-June-1
Hello Comet Observers!
After a few months of no bright comets, May brought a 9th magnitude comet in C/2016 M1 (PANSTARRS). This comet should continue to be the brightest this month though C/2017 T3 (ATLAS) may challenge it.
Bright Comets (magnitude < 10)
C/2016 M1 (PANSTARRS) – This dynamically old long-period comet was well observed in May with observers reporting it between magnitude 8.5 and 9.6 during the past week. It should continue to brighten by another 0.5 magnitudes this month as it approaches an August 10 perihelion at 2.21 AU. Increasing distance from the Earth after closest approach on June 24 at 1.29 AU will cause a slow fade beginning in late June.
Visual observations found the comet to have a fairly condensed coma (DC between 3 and 5) with a diameter between 3′and 5′. No visual reports of a tail have been made though the coma was observed to be slightly elongated.
The comet’s 91 degree inclination orbit is resulting in a steady southward motion from a June 1 declination of -24 degrees to -46 at the end of the month. It will be seen moving among the stars of Sagittarius, Corona Australis and Ara. A few close approaches to deep space objects will occur this month (Jun 9 – globular cluster M54 and Jun 12/13 – globular cluster M70).
C/2016 M1 (PANSTARRS)
T = 2018-Aug-10 q = 2.21 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-06-01 9.2 19 15 -24 24 2.353 1.463 142M Sgr
2018-06-11 8.9 18 53 -31 41 2.317 1.349 156M Sgr
2018-06-21 8.8 18 21 -39 26 2.285 1.293 163M CrA
2018-07-01 8.7 17 39 -46 24 2.259 1.301 153E Ara
C/2017 T1 (ATLAS) – It is questionable whether or not this comet will be observable and, if so, how bright it will be this month. C/2017 T1 (ATLAS) was discovered by the Hawai’i-based ATLAS (Asteroid Terrestrial-impact Last Alert System) project on October 14, 2017 at 18th magnitude. At the time the comet was located 4.0 AU from the Sun.
A dynamically-old short-period comet, ATLAS was brightening at a slightly faster than expected rate (2.5n ~ 11 compared to 2.5n ~ 10 which is usually, and often incorrectly, assumed for all long-period comets). This month, southern hemisphere observers may be able to reacquire the comet as it slowly moves away from the Sun in the morning sky. Since the comet has been out of view since April, its currently brightness is uncertain. Assuming (and we know the old saying about making assumptions) the comet has continued to brighten at its pre-April rate, the comet may be as bright as magnitude 9.4 by the end of the month.
Perihelion occurs on July 19 at 0.83 AU though the comet will be a rather distant 1.4 AU from the Earth at that time. With the same caveat about the assumption made above, the comet may peak around magnitude 8.6 around the time of perihelion. For southern hemisphere observers, the comet will be visible at a low elevations (~10 – 15 degrees in July). Unfortunately, it will be unobservable for northern hemisphere observers till the very end of the year when it will be a faint object (~16th magnitude).
C/2017 T3 (ATLAS)
T = 2018-Jul-19 q = 0.83 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-06-01 11.4 03 47 +20 43 1.204 2.184 10M Tau
2018-06-11 10.7 04 14 +16 40 1.084 2.026 15M Tau
2018-06-21 10.0 04 44 +11 39 0.978 1.857 20M Ori
2018-07-01 9.4 05 18 +05 24 0.893 1.685 26M Ori
Faint Comets (between magnitude 10 and 13)
21P/Giacobini-Zinner – Many long-time observers may remember this comet’s last excellent return in the fall of 1985 just as Comet Halley was approaching its February 1986 perihelion. This year marks G-Z’s 16th observed return since its visual discovery in 1900 by Michel Giacobini (Nice, France). The comet was visually re-discovered 2 returns later in 1913 by Ernst Zinner (Bamberg, Germany), hence the double appellation. Perihelion and closest approach to Earth both occur on September 10 at 1.01 AU and 0.39 AU, respectively. This will be the comet’s closest approach to Earth since 1959 when it passed 0.35 AU from Earth.
Recent observations place 21P between magnitude 13.8 and 15.1 over the last week of May. This month the comet is high in the morning sky (for northern observers) as it moves through Cygnus. It should rapidly brighten from around magnitude 13 to 11 over the course of the month. A peak brightness of around magnitude 7 is predicted for early September. Though the comet will be located at high northern declinations over the next few months, it will travel far enough south for most southern hemisphere observers by mid-September.
21P/Giacobini-Zinner
T = 2018-Sep-10 q = 1.01 AU Short-Period comet Period = 6.5 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 13.2 20 29 +33 15 1.682 1.157 101M Cyg
2018-06-11 12.5 20 46 +38 43 1.590 1.045 100M Cyg
2018-06-21 11.8 21 05 +44 23 1.498 0.943 99M Cyg
2018-07-01 11.1 21 28 +50 08 1.409 0.849 97M Cyg
48P/Johnson – 48P/Johnson has a large perihelion distance for a relatively bright short-period comet. Perihelion (2.00 AU) and closest approach to Earth (1.01 AU) occur within a week of each other in mid-August making this as good a return as possible for 48P. The comet should brighten from around magnitude 13 to 12 this month as it moves among the stars of Capricornus in the morning sky. This year marks its 11th observed return since it was discovered in 1949 by Ernest L. Johnson on photographs taken at the Union Observatory in Johannesburg, South Africa.
The brightest report from May was by the Catalina Sky Survey which placed Johnson at magnitude 14.8 on May 21. This is about 1.5 magnitudes fainter than the predicted magnitude. If the comet continues to run fainter than predicted, the magnitudes below may be too bright.
48P/Johnson
T = 2018-Aug-12 q = 2.00 AU Short-Period comet Period = 6.5 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 12.9 21 53 -14 58 2.084 1.580 104M Cap
2018-06-11 12.6 22 07 -15 08 2.064 1.465 111M Aqr
2018-06-21 12.2 22 19 -15 36 2.047 1.359 118M Aqr
2018-07-01 11.9 22 28 -16 26 2.032 1.263 125M Aqr
66P/du Toit – Short-period comet 66P/du Toit is still running brighter than predicted. Observers have been estimating it to be between magnitude 10.2 and 10.7 during the last week of May. The comet possesses a large, low surface brightness coma so the comet may appear fainter than expected to some observers. The comet remains a very difficult object for northern hemisphere observers. Personally, I have not been able to acquire it in my 30×125 binoculars due to a combination of its low elevation and a brightening dawn sky. This marks 66P’s 4th observed and best apparition since its discovery by South African astronomer Daniel du Toit in 1944. The next return won’t be till 2033 though with a minimum comet-Earth distance of 1.36 AU it should be a fainter object at that return.
66P/du Toit
T = 2018-May-19 q = 1.29 AU Short-Period comet Period = 14.9 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 10.7 23 54 -30 48 1.302 0.903 85M Scl
2018-06-11 11.1 00 23 -27 41 1.326 0.911 86M Scl
2018-06-21 11.7 00 46 -24 49 1.363 0.918 89M Scl
2018-07-01 12.4 01 03 -22 15 1.410 0.923 93M Cet
364P/PANSTARRS – 364P/PANSTARRS is an example of a low activity comet. Similar to other comets of this type (such as 169P/NEAT, 249P/LINEAR and 300P/Catalina), 364P is only active at small heliocentric distances. Whether this is due to age, evolution or the possibility that these objects originated in the asteroid Main Belt rather than the Kuiper Belt, is still TBD.
Discovered in 2013 as P/2013 CU129, it is making its second observed return. This comet has a rather short period (4.9 years) and is only active for a few months around perihelion. Perihelion occurs this month on the 24th at 0.80 AU from the Sun. The comet displayed a thin tail in May though it didn’t possess much of a coma. CCD and large aperture visual observers can watch the comet approach and pass through perihelion this month. Northern observers will lose sight of the comet mid-month (regaining the comet in early September) while southern observers will have an uninterrupted view of the comet (though it will get very low in early July).
364P/PANSTARRS
T = 2018-Jun-24 q = 0.80 AU Short-Period comet Period = 4.9 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 13.7 08 55 +20 08 0.883 0.530 60E Cnc
2018-06-11 12.5 08 56 +13 55 0.827 0.447 52E Cnc
2018-06-21 11.5 08 47 +05 45 0.800 0.362 44E Hya
2018-07-01 10.9 08 18 -04 58 0.805 0.290 37E Hya
C/2016 N6 (PANSTARRS) and C/2016 R2 (PANSTARRS) – In addition to C/2016 M1, there are two other PANSTARRS long-period comets with relatively large perihelion distances visible this month. Both are early evening objects located north of the ecliptic. C/2016 R2 passed perihelion on May 2 at 2.60 AU. It is approaching solar conjunction this month though its location north of the ecliptic means it should remain observable though at low elevations through conjunction. C/2016 N6 reaches perihelion on July 18 at 2.67 AU. The comet will be become a more difficult object to observe as the month progresses and should be lost to most observers towards the end of the month. C/2016 R2 will spend the month around magnitude 11 while C/2016 N6 will be around magnitude 12.
C/2016 R2 (PANSTARRS)
T = 2018-May-02 q = 2.60 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-06-01 11.1 06 22 +48 36 2.613 3.389 34E Aur
2018-06-11 11.1 06 47 +49 55 2.625 3.426 32E Lyn
2018-06-21 11.2 07 15 +51 00 2.641 3.455 31E Lyn
2018-07-01 11.2 07 44 +51 51 2.661 3.476 31E Lyn
C/2016 N6 (PANSTARRS)
T = 2018-Jul-18 q = 2.67 AU Long-Period comet - dynamically old
Date Mag R.A. Decl. r d Elong const
2018-06-01 12.0 07 56 +46 08 2.715 3.297 47E Lyn
2018-06-11 12.1 08 02 +42 39 2.698 3.401 39E Lyn
2018-06-21 12.1 08 08 +39 25 2.684 3.491 32E Lyn
2018-07-01 12.1 08 15 +36 23 2.675 3.565 24E Lyn
Other Comets of Interest
Low activity comet (3552) Don Quixote is still designated an asteroid even though Spitzer Space Telescope observations from 2009 showed a faint coma and tail. This month Don Quixote is near its 2018 peak at around 16th magnitude. The object is steadily moving north in the morning sky and is now observable by observers at northern mid-latitudes.
(3552) Don Quixote
T = 2018-May-07 q = 1.24 AU Short-Period comet Period = 8.8 yr
Date Mag R.A. Decl. r d Elong const
2018-06-01 15.9 01 04 -02 58 1.280 1.511 56M Cet
2018-06-11 15.9 01 25 +02 48 1.317 1.507 59M Psc
2018-06-21 16.0 01 44 +08 22 1.365 1.501 62M Psc
2018-07-01 16.0 02 01 +13 44 1.422 1.493 65M Ari
Looking ahead, the later months of 2018 will see a few other comets reaching magnitude 10 or brighter. 38P/Stephan-Oterma was observed back in the summer of 2017 by Pan-STARRS at 21st magnitude. CCD observers have recently observed it at 17th magnitude now that it is coming out of solar conjunction. 64P/Swift-Gehrels was detected for the first time this apparition by Spacewatch on May 25 UT at magnitude 20.7. What should be this year’s brightest comet, 46P/Wirtanen, was picked up by the Discovery Channel Telescope on May 8 UT at magnitude 20.3.
Dynamically new and intrinsically faint C/2017 S3 (PANSTARRS) has shown a very slow intrinsic brightening since its September 2017 discovery (2.5n ~ 5.5!). Perihelion occurs on August 15 at a small distance of 0.21 AU. Though the comet will be located too close to the Sun at that time, there is hope it could become bright (7th-8th magnitude) before becoming lost in the glare of the Sun. In mid-May the comet brightened to 15-16th magnitude. Extrapolating it’s slow brightening trend suggests the comet will not be a bright visual object prior to becoming lost in the bright twilight sky. Then again the comet may brighten at a faster rate, especially if gas-rich, as it gets closer to the Sun. A major question remains as to whether it will be a bright visual object prior to perihelion. Being intrinsically faint and dynamically new there is also a real possibility that this comet’s nucleus is small and will disintegrate at it nears the Sun.
C/2017 S3 (PANSTARRS) T = 2018-Aug-15 q = 0.21 AU Long-Period comet - dynamically new Date Mag R.A. Decl. r d Elong const 2018-06-01 15.7 01 09 +57 25 1.788 2.242 51M Cas 2018-06-11 15.3 01 40 +58 23 1.614 2.030 51M Cas 2018-06-21 14.7 02 16 +59 09 1.430 1.803 52M Cas 2018-07-01 14.1 03 01 +59 24 1.237 1.562 52M Cas
As always, the Comet Section is happy to receive all comet observations, whether images, drawings, magnitude estimates, and even spectra. Please send your observations via email to < carl.hergenrother @ alpo-astronomy.org >.
- Carl Hergenrother (ALPO Comet Section Coordinator)
