COMET HIGHLIGHTS FOR SEPTEMBER 2013
2013-September-04
Comet action starts to really pick up this September. Though only one comet is currently brighter than magnitude 10, the ’stars’ of the Fall are rapidly brightening and can be followed via CCD imaging and large aperture visual observing.
C/2012 V2 (LINEAR)
C/2012 V2 is a nice surprise comet that has become much brighter than expected. Observations over the past few weeks show it to be between magnitude 8 and 9. It reached perihelion on August 16 at a distance of 1.45 AU from the Sun. Even though it is past perihelion it should only fade slowly this month, still being brighter than 9.0 to 9.5 by the end of the month. The comet is only visible from the Southern Hemisphere as it tracks southeastward along the border of Hydra and the constellations of Puppis, Pyxis and Antlia.
Inbound Comets
C/2012 S1 (ISON)
After passing solar conjunction this summer, Comet ISON (T = 2013 Nov 28, q = 0.01 AU) is once again observable. There has been much discussion on how bright the comet really is with magnitude estimates that range from 11th to 15th magnitude. It seems the consensus is around magnitude 13. A big reason for the discrepancy was ISON’s location very low in the eastern sky during dawn in August. This month the comet will be observable at a more convenient elevation before the start of dawn. Hopefully we’ll have a better understanding of its brightness over the next few weeks.
The comet will be a morning object this month as it moves from just north of the Beehive Cluster in Cancer and into Leo by month’s end. Assuming the comet is around magnitude 13 at the start of the month, it should brighten to between magnitude 11.5 and 12.0 by the end of the month. On the 1st ISON will be 2.18 AU from the Sun and 2.97 AU from Earth. By the end of the month the comet will be 1.65 AU from the Sun and 2.15 AU from Earth. An added bonus for early morning observers will be the comet’s proximity to Mars at the end of the month. ISON will pass within 0.07 AU of Mars on October 1 resulting in the comet being located within a few degrees of Mars for a few days. Many of the spacecraft on and around Mars will be imaging the comet at that time.
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.
2P/Encke
If ISON is a new comet inbound for the first time in billions of years, the other bright comet of the Fall is its opposite. 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 1.58 AU from the Sun and ends the month 1.15 AU out. Its geocentric distance closes from 1.16 to 0.60 AU. The most recent visual observations place the comet around magnitude 14 which agrees well with its behavior in the past. The comet should continue to rapidly brighten this month and be around magnitude 12.6 on the 11th, 11.3 on the 21th and 9.7 by October 1 as it leaves Perseus and traverses Auriga. We also request ALPO observers make a concerted effort to observe Comet Encke during the next few months leading up to its perihelion.
C/2012 K1 (PANSTARRS)
While ISON may be getting all of the headlines due to the possibility of it becoming a brilliant object, C/2012 K1 is actually a much brighter comet intrinsically (T = 2014 Aug 27, q = 1.06 AU). Based on recent CCD observations C/2012 K1 is intrinsically ~2 magnitudes brighter than ISON and very similar in brightness to C/2011 L4 (PANSTARRS) at a similar distance from the Sun (5.2 AU). Current projections have it reaching 5-6th magnitude next summer which is impressive considering the comet will be located over 2 AU from Earth on the other side of the Sun at the time. We can only imagine how bright this comet would be if it came closer to Earth.
This month the comet decreases its heliocentric distance from 4.74 to 4.45 AU from the Sun. Even at this distance, it is ~13-14th magnitude and already showing significant jet activity.
Similar to ISON, K1 is a dynamically new comet. Such comets routinely brighten rapidly when far from the Sun only to see their rate of brightening slow, stall or even turn into a fading trend as they get closer to the Sun. Observers are encouraged to monitor K1 as it nears the heliocentric distances when C/2011 L4 and C/2012 S1 experienced their change in brightening.
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)
