ALPO COMET NEWS FOR DECEMBER 2016
With 2016 drawing to a close, it is a good time to look back on the comet year that was. The brightest comets of 2016 were 252P/LINEAR (mag 4), C/2013 US10 (Catalina) (mag 6), C/2013 X1 (PANSTARRS) (mag 6), and C/2014 S2 (PANSTARRS) (mag 8). Before the year ends, two more comets may work their way onto the list. Though comet 45P/Honda-Mrkos-Pajdusakova will be a much easier target to observe in February, observers with a good southwestern horizon may peak a glimpse of it rapidly brightening this month. C/2016 U1 (NEOWISE) is surrounded by some uncertainty, but recent observations suggest this comet will become bright enough for visual observers this month as well.
During November, CCD observers Denis Buczynski and Gianluca Masi contributed images of 56P/Slaughter-Burnham, 74P/Smirnova-Cherynkh, 117P/Helin-Roman-Alu, 128P/Shoemaker-Holt, 226P/Pigott-LINEAR-Kowalski, C/2010 U3 (Boattini), C/2013 US10 (Catalina), C/2013 V4 (Catalina), P/2015 TP200 (LINEAR), C/2015 V1 (PANSTARRS), C/2015 V2 (Johnson), C/2015 VL62 (Lemmon-Yeung-PANSTARRS), and C/2016 T3 (PANSTARRS). Also, visual observer Per-Jonny Bremseth has been contributing his extensive collection of excellent comet drawings going back to C/1969 Y1 (Bennett).
45P/Honda-Mrkos-Pajdusakova [Perihelion on 2016 December 31 at 0.53 AU]
Comet 45P/Honda-Mrkos-Pajdusakova… Honestly, that is the kind of name a comet should have. When 45P was discovered back in 1948, comets were routinely named after three discoverers. That practice has fallen out of favor. In fact, no new discoveries in 2016 even share two names. The two tri-named comets mentioned above (Lemmon-Yeung-PANSTARRS and Pigott-LINEAR-Kowalski) represent the only comets named after three discoverers since 2003.
Comet 45P/Honda-Mrkos-Pajdusakova is out best bet to break our recent bright comet drought. 2016 will be the 12th observed apparition for 45P as it rounds the Sun once every ~5.3 years. It is one of a class of Jupiter-family comets that have small perihelion distances but are only active (and bright) when close to the Sun. As December begins, the comet is around 11th to 12th magnitude. It will be around 9th magnitude by the middle of the month and 7th magnitude by the end. Observing this comet will still be difficult as it is usually very diffuse (as is typical for a gaseous comet) and located low in the southwestern sky during the evening as it traverses Sagittarius (Dec 1-14) and Capricornus (14-31). For observers at 40N, the comet will only be located at an elevation of ~10 degrees at the end of astronomical twilight all month long. After solar conjunction in early February, 45P will rapidly climb into the morning sky as a 7th-8th magnitude object as it passes within 0.08 AU of Earth. This month, its heliocentric and geocentric distances decrease from 0.81 to 0.53 AU and 1.27 to 0.68 AU, respectively.
2P/Encke [Perihelion on 2017 March 10 at 0.34 AU]
Comet Encke is back again and making its 63rd observed apparition since it was first seen in 1786. Encke will be a visual object this February as it brightens to 7th magnitude. This month, the comet is only of interest to CCD imagers as it rapidly brightens from ~17th to 14th magnitude. The Section asks that CCD imagers start following Encke now so we can watch it brighten and develop as it travels towards perihelion. An interesting imaging activity is to monitor the development of its coma in different colors. In the past, the gas coma has developed faster than the dust coma so Encke appeared to have a large coma in a blue filter while still appearing inactive in a red filter. This month Encke is an evening object moving through Pisces at an elongation that drops from 97 to 68 degrees. It distance from the Sun decreases from 1.79 to 1.39 AU while its geocentric distance increases slightly from 1.37 to 1.42 AU.
C/2015 V2 (Johnson) [Perihelion on 2017 June 12 at 1.64 AU]
Jess Johnson of the Catalina Sky Survey discovered this long period comet on November 3, 2015 with the 0.68-m Catalina Schmidt. The comet is inbound with a perihelion of 1.64 AU and close approach to Earth at 0.81 AU this summer. It is well placed for northern observers through perihelion. Now is a good time for CCD imagers and large aperture visual observers to watch C/Johnson brighten from its current 12th magnitude to a peak of 6-7th magnitude. This month, it is a morning object in Canes Venatici (Dec 1-19) and Bootes (19-31) at an elongation that increases from 79 to 89 degrees. It starts the month 2.93 AU from the Sun and 2.96 AU from Earth. At the end of the month, these values decrease to 2.64 AU from the Sun and 2.47 AU from Earth.
C/2016 U1 (NEOWISE) [Perihelion on 2017 January 14 at 0.32 AU]
The discovery of this comet was announced in the previous ALPO Comet News. Initially reported as very faint by most CCD astrometrists, recent CCD and visual observations show it to be much brighter than originally thought. At the end of November, C/NEOWISE is around 11-12th magnitude. With perihelion on January 14 at a very small distance of 0.32 AU, the comet may brighten to 7-8th magnitude before getting too close to the Sun in early January. This month, C/NEOWISE travels through Canes Venatici (Dec 1-3), Bootes (3-12), Corona Borealis (12-16), Serpens (16-17), Hercules (17-24), and Ophiuchus (24-31) in the morning sky as its heliocentric distance drops from 1.13 to 0.49 AU and its geocentric distance from 0.77 to a minimum of 0.71 on Dec 12/13 before growing to 0.71 AU at the end of the month.
Amazingly since the last Comet Section News posting, no comet discoveries have been officially reported. That said, an asteroid on a very cometary orbit was announced.
2016 VY17 is on Halley-type orbit with a retrograde inclination of 148 deg and period of 37.5 years. Perihelion will occur in early July at 1.66 au and closest approach to Earth follows in mid-August at 0.89 au. If the object is truly inactive it will brighten to 17th magnitude in mid-August. It is very possible that VY17 will become active and if so, it could become bright enough for visual observation. CCD observers are encouraged to monitor this object and send your images and photometry to the Comet Section. Who knows, maybe you will be the first to notice VY17 as an active comet.
As always, the Comet Section is happy to receive all comet observations, whether images, drawings or magnitude estimates.
- Carl Hergenrother (ALPO Comet Section Coordinator)