Comet Expected to Have Close Encounter with Sun on Thanksgiving

As comet ISON hurtles toward its close encounter with the sun on Thanksgiving Day, astronomers don't know if it will put on a spectacular light show or fizzle out.

The icy chunk of space rock is making its first-ever pass around the sun, which means it still contains pristine matter dating from the earliest days of the solar system, according to NASA.

ISON -- named after the International Scientific Optical Network -- was unusually bright when first spotted beyond the orbit of Jupiter in 2012.

"Based on this, astronomers predicted comet ISON would outshine the full moon by a factor of more than 100," according to a Griffith Observatory statement. "Since those early predictions, comet ISON has failed to deliver as promised. Early in 2013, it was already evident that the comet is not brightening according to predictions."

Some astronomers theorize ISON may be on the verge of disintegrating, and the fly-by of the sun could hasten the process.

"We have never seen (this comet) interact with the sun's heat before so we have no prior experience to help us predict how it will fare," the Griffith Observatory statement continued. "... Astronomers still don't know whether ISON will be the comet of the century or a dud."

The comet's expected trajectory will take it to within 727,000 miles of the sun on Nov. 28.

"There is a chance that comet ISON could disintegrate entirely from the interaction," according to the observatory. "There is also some chance, if it does survive, that it will brighten significantly."

If the latter happens, the comet could be visible "in broad daylight," according to the Griffith Observatory.

The observatory plans to hold an early morning public viewing in early December, assuming ISON "survives and thrives."

- City News Service