This is Comet C/2012 S1 (ISON), currently out past the orbit of Jupiter. Believe it or not, all of those letters and numbers actually mean something. The C/ means that it is a long-period comet, originating in the very distant Oort Cloud rather than the less distant Kuiper Belt just past the orbit of Neptune. Long-period comets return only after thousands or even millions of years, and if they get too close to Jupiter, they can be kicked out of the Solar System entirely.
2012 is the years that the comet was discovered. The S1 means that it was the first comet discovered in period S, which is the second half of September. Finally, ISON is the discoverer: the International Scientific Optical Network, based near Kislovodsk, Russia.
The cool part is that next fall (November 29, 2013, to be precise), Comet ISON will come very close to the Sun. How close? This close:
This cartoony image is, in fact, to scale. That’s not comet ISON, of course–it’s Comet NEAT from 2004–but a comet’s coma (the bright, but diffuse cloud that surrounds the tiny nucleus) really can grow larger than Jupiter, and comets really can survive passing that close to the Sun, even though they’re made of ice.
Comet ISON is making headlines because astronomers predict that it could become very bright. There’s a chance–but only a chance–that around Christmas next year, Comet ISON will light up brighter than the full Moon, making it the brightest comet ever seen since accurate records have been kept. Of course, there’s also a chance that it could remain invisible to the naked eye, like Comet Elenin in 2011. Comets are notoriously fickle, and predictions have been known to be way off.
Even so, I think that Comet ISON is well worth watching over the next year. The last two really bright comets, Comet Lovejoy in 2011 and Comet McNaught in 2007, were mostly visible only in the southern hemisphere, but Comet ISON will be visible in the northern sky in the hours before sunrise, so North America will get a front row seat.
There will be one other chance to see a comet next year. During next March and April, Comet C/2011 L4 (PANSTARRS) may be visible throughout much of the world shortly after sunset. It’s not likely to be super-bright, but it could become the equal of Comet Hyakutake in 1996 and Comet Hale-Bopp in 1997, both of which were pretty cool. I highly recommend Space Weather to keep up with news about comets, meteor showers, auroras, and anything else that’s going on in the sky.
And keep looking up. There’s plenty to see whenever the sky is clear.