Comet Section        




We are still in the midst of a bright comet drought this month. While there have been no visual magnitude estimates submitted to the ALPO Comet Section since July, CCD observers have been busy imaging some of the fainter comets. During October, Richard Owens and Gianluca Masi contributed images of 2P/Encke, 53P/Van Biesbroeck, 93P/Lovas, 174P/Echeclus, C/2014 A4 (SONEAR), C/2016 A8 (LINEAR), and C/2016 M1 (PANSTARRS). Though no comets are expected to be brighter than magnitude 11-12 in November, there are some comets that will become bright during the coming months that would benefit from CCD imaging now as they brighten.

Evening Comets

45P/Honda-Mrkos-Pajdušáková [Perihelion on 2016 December 31 at 0.53 AU]

2016 will be the 12th observed apparition for Comet Honda-Mrkos-Pajdušáková as it rounds the Sun once every ~5.3 years. As November begins, there have been no reported observations of this comet. Historically, 45P brightens rapidly when close to the Sun and should be ~17th magnitude. The lack of observations may be its location very low in the evening sky as it traverses Sagittarius. CCD users imaging Venus and Mars can try to go a bit deeper for 45P as it should brighten to 12th magnitude by the end of the month. Visual observers will be able to observe 45P very low in the evening sky starting in December through early January as it brightens to 7th magnitude. 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 1.23 to 0.81 AU and 1.57 to 1.27 AU, respectively.

2P/Encke [Perihelion on 2017 March 10 at 0.34 AU]

Comet Encke is back again. In fact, it never really ‘leaves’ in that it is visible even at aphelion if one can image down to ~20th magnitude. 2017 will mark Encke’s 63rd observed apparition since it was first seen in 1786. The high number of returns is due not only to Encke’s long observational history but also due to it having the shortest known cometary orbital period at 3.3 years. 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 will be ~17th magnitude. The Section asks that CCD imagers start following Encke now so we can watch it brighten and develop as it heads 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 Pegasus (Nov 1-7) and Pisces (7-30) at an elongation that drops from 134 to 97 degrees. It distance from the Sun decreases from 2.12 to 1.79 AU while its geocentric distance increases slightly from 1.30 to 1.37 AU.

Morning Comets

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 to a perihelion of 1.64 AU and close approach to Earth of 0.81 AU this summer. It is well placed for northern observers through perihelion. As a result, now is a good time for CCD imagers and large aperture visual observers to watch C/Johnson brighten from its current 13th magnitude to a peak of 6-7th magnitude. This month, it is a morning object in Canes Venatici at an elongation that increases from 67 to 79 degrees. It starts the month 3.21 AU from the Sun and 3.47 AU from Earth. At the end of the month, these values decrease to 2.93 AU from the Sun and 2.96 AU from Earth.

C/2016 U1 (NEOWISE) [Perihelion on 2017 January 14 at 0.32 AU]

This will be an interesting comet to watch over the coming few months. With perihelion on January 14 at a very small distance of 0.32 AU, there are hopes that this comet could become bright. Dampening those hopes is the fact that the comet is currently 1.6 AU from the Sun and still only 20th magnitude. This suggests that C/NEOWISE is intrinsically very faint. While it may brighten significantly as it approaches perihelion, it may not become bright enough for visual observation. While currently out of range for most CCD imagers, I’ll send out a mid-month Comet Section news update if the comet does brighten enough to warrant additional attention. This month, C/NEOWISE travels through Ursa Major into Canes Venatici in the morning sky as its heliocentric distance drops from 1.67 to 1.13 AU and its geocentric distance from 1.32 to 0.77 AU.

New Discoveries

Since the last Comet Section News posting, a number of new comets were discovered in addition to the already mentioned C/2016 U1 (NEOWISE).

C/2016 T3 (PANSTARRS) is one of three dynamically old long period comets (meaning this is not their first trip through the inner Solar System) discovered since the last Comet Section news update. C/2016 T3 was found by the Pan-STARRS program at 20th magnitude. With perihelion occurring on September 8, 2017 at 2.67 AU from the Sun, it may brighten by a few magnitudes to ~17.

C/2016 T2 (Matheny) is also a dynamically old long period comet with a perihelion distance of 1.92 AU and inclination of 81 degrees. It was 18th magnitude when Rose Matheny of the Catalina Sky Survey used the 1.5-m Mount Lemmon reflector first saw it on October 10. Perihelion occurs this December 27 when the comet will peak at 17-18th magnitude.

C/2016 T1 (Matheny) was also found by Rose Matheny with the Catalina Sky Survey 1.5-m Mount Lemmon reflector. This comet was found 4 days before C/2016 T2. The two comets are Matheny’s only comet discoveries. Similar to C/2016 T2, C/2016 T1 is a dynamically old long period comet but with a perihelion distance of 2.30 AU, perihelion date of February 2, 2017, and inclination of 129 degrees. It was 18th magnitude at discovery and may brighten another magnitude.

P/2016 S1 (PANSTARRS) is a short period comet first seen by Pan-STARRS on September 21. It is on a 24 year period orbit with a 94 degree inclination and a March 16, 2017 perihelion at 2.41 AU from the Sun. The comet may brighten to 17th magnitude from its discovery brightness of 19th magnitude.

P/2016 SV (PANSTARRS) is another short period comet with a 6.9 year period. It reaches perihelion on September 11, 2016 at 2.22 AU from the Sun. It was 19th magnitude when discovered by Pan-STARRS on September 19. Pre-discovery observations by Pan-STARRS from June 20 and the Catalina Sky Survey from 2009 were identified after discovery. It is unlikely this comet will get much brighter than 19th magnitude.

P/2016 R4 (Gibbs) was found by Alex Gibbs of the Catalina Sky Survey with the Mount Lemmon 1.5-m reflector. P/2016 R4 was first seen on September 10 at 18th magnitude. It has a 12.3 year period and passed perihelion on July 16, 2016 at q = 2.80 AU.

As always, the Comet Section is happy to receive all comet observations, whether images, drawings or magnitude estimates.

- Carl Hergenrother (ALPO Comet Section Coordinator)

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