Approaching comet may be brightest in a century

Posted by Emma Woollacott

A newly-discovered comet looks likely to blaze brightly in our skies late next year.

Comet C/2012 S1 (ISON), is due to come within 0.012 astronomical units (AU) of the sun - just 1.1 million miles - on 29 November 2013. How brightly it will shine is still hard to determine, as there's a chance it will just boil away completely, as comet Elenin did last year.

If it doesn't though, it could be brighter than any comet seen in the last hundred years - brighter than the full moon. If so, it should be visible with the naked eye for about two months, even during the daylight.

The comet is currently just past Jupiter, about 6.6 AU away. It appears to have originated in the Orrt cloud, from which many comets emanate, meaning that this would be its first approach to the sun.

"Comets sometimes 'turn on' when they get to about 2.5 AU, suddenly increasing in brightness," astronomer Bill Gray tells The Planetary Society. "If we're lucky, that'll happen for this object. It'll reach 2.5 AU in August 2013."

Its closest approach to the Earth will occur on 28 December next year, when it will come within 0.43 AU.

The comet was discovered late last week using the International Scientific Optical Network's 16-inch (0.4-meter) Santel reflecting telescope in Russia.

Comet researcher John Bortle has pointed out that the trajectory of the comet is very similar to that of the Great Comet of 1860, leading him to suggest that the two might once have formed part of the same object.

"The Great Comet of 1680 had a supposed e of 0.999986. Should comet 2012 S1 begin to show an e of anything less than 1.0 in coming months I think that the conclusion that the two comets are at least in some manner directly related becomes almost inescapable," he says.

"Purely as speculation, perhaps the two bodies could have been one a few revolutions ago."