Comet Ison, a sun-grazing comet, will put on a good show for astronomers in November. Whether it survives to amaze all of us in December is still uncertain.

Adam Block/University of Arizona/Mount Lemmon Sky Center

Comet Ison is looking pretty good as it approaches the sun, with a big, long tail and a greenish hue.

Astronomers still don't know if it will survive this passage intact and have enough volatiles left to become the "comet of the century" in December or even "the comet of the year.

Predictions range from spectacular to disappearing.

Astronomer Jian-Yang Li, of Tucson-based Planetary Science Institute, said he can't predict what the comet will look like in late December when it's closest to Earth, but he's fairly certain it will be spectacular as it approaches the sun in late November.

The photo accompanying this post, taken by astrophotographer Adam Block at the Mount Lemmon Sky Center, shows it looking pretty good already.

Li said his observations have determined that one side of the comet, which may hold lots of frozen volatile material, has yet to be exposed to the sun's influence.

Li's calculations of the comet's rotation, presented Wednesday at the American Astronomical Society’s Division for Planetary Sciences annual meeting in Denver, predict it will expose that hidden side a week before it reaches its closest point to the sun on Thanksgiving, Nov. 28.

That should produce a "good show" for astronomers with access to solar telescopes capable of looking so close to the sun.

Some of Li's colleagues will be observing Comet Ison from the McMath-Pierce Solar Telescope atop Kitt Peak when it reaches its closest point on Thanksgiving Day.

Astronomer Matthew Knight of Lowell Observatory said three teams of astronomers will be sharing the venerable instrument between November 23 and December 4.

What comes after that is anybody's guess.

Knight said he expects the long dust tail of the comet to be visible to the naked eye in the Northern Hemisphere, even if its nucleus disintegrates.

But he also doesn't expect that to happen. He is presenting a paper at the planetary conference tomorrow that predicts it will survive intact, based on observations he and colleagues made at Lowell's newly commissioned Discovery Channel Telescope south of Flagstaff.

The behavior of comets is tough to predict, he said, but his bet is that this one will put on a show.