The Great Comets (Maybe) of 2013


2013 could be the best year for comets since 1996-1997 when  Hyakutake, and  Hale-Bopp made their appearances. Two potentially naked eye comets are being tracked. One may be visible in March and the other in December.

Disclaimer: Predictions like this are always made with apprehension. Sometimes they fail to meet brightness predictions, and sometimes they don’t look as expected. There are four types of comets: those that fail to match predictions, those that unexpectedly perform, those that perform as expected, and those that perform as expected but are hard to see anyway.

There are two types of bright comets: those that pass near the sun, and those that pass near the Earth. Bright comets that give off lots of dust and gas near perihelion are at their best in either the morning or evening as they approach, or recede from, the sun. These may easily visible for days or a couple weeks. They may have great tails. But they have to be extremely bright to be visible near the sun.   Some extremely bright comets have only been visible by satellite. <note: link may be intermittent??>

Near Earth comets may not be especially visible. They may be bright, but are diffuse and may be difficult to see. Hyakutake (1996) was a happy exception. They also tend to travel through the sky quickly, with the position changing significantly night to night. They may be bright for only a few days, or a week. Tracking these comets provide an opportunity for the observer to learn the constellations that the comet passes through. Binoculars are helpful in seeing the comets more clearly.

A way to estimate the brightness of a comet is to compare it to nearby stars. Binoculars help here. Defocus the binoculars so that stars are about a large as the comet. Then stars that are a little dimmer `and/or a little brighter can be identified and star charts consulted to bracket and interpolate the brightness.

 PanSTARRS (C/2011 L4) reaches perihelion March 10, at 0.3 au from the sun, and a magnitude of maybe 2. From the March Sky and Telescope, it will be best for the Northern Hemisphere about March 8-20, when it may still be brighter than 5, difficult to see in the dusk sky. A good observation time is 30-60 min after sunset. I predict that in Cleveland it will be cloudy if it reaches naked eye intensity, so take any opportunity for clear skies to look for it. It should be possible to track into early April.

 Comet ISON (C/2012 S1) will reach perigee at 0.4 a.u. from Earth Dec 27, a few weeks after perihelion (0.01 au, Nov 28).  It could be a Christmas Comet as it moves through Hercules Its orbit it similar to that of the Great Comet of 1680 which raises hope for a great apparition.

Occasionally I have the opportunity to judge science fair projects, and now is the season. However, I rarely see astronomy projects. The March comets provide an opportunity to see what comets are like, and do some research, preparing and modifying a hypothesis in preparation for the fall comet. A hypotheses about “published” predictive light curves, compared to your observations, might make a suitable project. Or comparing your observations to those of other observers might be fun. Successfully taking photographs of a comet, and showing its evolution, should be worth a few at-a-boys/girls

Update on PanSTARRS:

via http://www.aerith.net predicted light curve/data

PanSTARRS light curve observation/predictions

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