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.
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)
