COMET HIGHLIGHTS FOR OCTOBER 2013
2013-October-04
By the end of October as many as 4 comets may be brighter than 10th magnitude. With three still inbound, they will be even better next month.
Comet Spotlight
C/2012 S1 (ISON)
No question about it, Comet ISON (T = 2013 Nov 28, q = 0.01 AU) is the comet everyone is waiting for. Whether ISON will be the ‘Comet of the Century’ or even the ‘Comet of the Year’ remains to be seen. Visual and V-band CCD images from early October show the comet to be around magnitude 11.5. There has been much discussion on various comet related lists about whether the comet is brightening or even starting a terminal fade. Observations by your Comet Section co-coordinator show the split personality of the comet with V-band measurements showing a rapidly brightening comet and R-band images showing little brightening over the past few weeks. R-band samples primarily dust while V-band sees a heavy gas component so perhaps the comet is becoming more gas-rich, or dust-poor depending on your view.
ISON is a morning object as it moves through Leo only a few degrees north of Mars. We should expect it to brighten from its current magnitude 11.5 to around magnitude 8 or 9 by the end of the month. At the start of October the comet was located 1.65 AU from the Sun and 2.15 AU from Earth. By month’s end it will be 1.02 AU from the Sun and 1.26 AU from Earth.
It is still too early to say with any certainty what the ultimate brightness of ISON will be at perihelion, or even if it will survive to see perihelion for that matter. The Comet Section requests that ALPO observers make a concerted effort to observe Comet ISON as soon and as often as possible. Please visual magnitude estimates, drawings and images to the undersigned. We would also like to receive any FITS images in order to obtain standard photometry.
Inbound Comets
2P/Encke
There are two other inbound comets that should brighten enough to be seen without imaging equipment. Comet 2P/Encke (T = 2013 Nov 21, q = 0.34 AU) has the shortest known cometary period at 3.3 years. Since it was first seen in 1786, the comet has been observed to orbit the Sun over 60 times. The comet is starting the month at 1.5 AU from the Sun and ends the month 0.64 AU out. Its geocentric distance reaches a minimum of 0.48 AU on October 16/17. The most recent visual observations place the comet between magnitude 9.5 and 11.5. The large scatter in estimated brightness is likely due to the comet having a very large, low surface brightness coma which is typical of Encke. The comet should continue to rapidly brighten this month and be around magnitude 7 by the end of the month. Encke is also a morning object as it speeds through the constellations of Auriga, Lynx and Leo Minor. We request ALPO observers make a concerted effort to observe Comet Encke during the next few months leading up to its perihelion.
C/2013 R1 (Lovejoy)
This one is a new discovery. On September 7 Terry Lovejoy, an amateur astronomer from Queensland, Australia, discovered comet C/2013 R1 (Lovejoy) on CCD images taken with a HyperStar equipped 8″ SCT. The comet will close to within 0.40 AU of Earth on November 19/20 and perihelion on December 22 at a distance of 0.81 AU from the Sun. Located at distances of 1.61 AU from the Sun and 1.28 AU from Earth, the comet is currently being observed at magnitude 10.5. It is very possible Lovejoy may become a borderline naked eye visible comet in late November/early December at the same time that ISON is also (hopefully) visible to the naked eye as well. FYI, both comets will be morning objects. We ask that ALPO observers also make observations of Comet Lovejoy.
Outbound Comets
C/2012 V2 (LINEAR)
This one is only for southern hemisphere observers. C/2012 V2 (T = 2013 Aug 16, q = 1.45 AU) is currently between magnitude 9.0 and 10.0. It should fade by a magnitude by the end of the month as it moves from 1.59 to 1.80 AU from the Sun and 2.09 to 2.27 AU from Earth. The comet will be moving through Antila, Vela and Centaurus this month.
The Section is always collecting observations (both visual and CCD) and magnitude estimates for all comets. An image gallery has been set up and now contains images of 40 different comets.
All ephemerides/positions for the above comets and all other comets can be generated at the Minor Planet Center and JPL/Horizons websites.
- Carl Hergenrother (Comet Section Acting Co-Coordinator)
