Sizzle. Or fizzle. The performance of comets cannot be accurately predicted. They can fascinate or disappoint scientists and observers. But scientists have high hopes for the comet ISON.
On Nov. 28, 2013, the head of the comet passes 800,000 miles (1.2 million kilometers) above the sun's surface. This is closer to the sun's surface than the sun's own diameter. If it survives its close brush with the sun without breaking up, Comet ISON will make a hairpin turn past the sun, whipping around onto the outbound leg of its orbit. The comet could provide a spectacular display in Earth’s skies in November and December.
Astronomers have high hopes because Comet ISON seems to be a new comet fresh from the Oort cloud, a zone of deep-frozen objects orbiting in the dark outlands of our solar system. The most optimistic prediction is that Comet ISON could rival the Great Comet of 1680.
Comet ISON is believed to be making its first trip to the sun, and so is hoped to still have most of its volatiles intact. Volatiles are the substances which heat up and blast off the comet's nucleus to form the wispy comet tail which can stretch for millions of miles through space. Reference