5 things to know about Comet ISON

Story highlights

  • Comet ISON discovered in September, should pass within Earth's view this year
  • Hubble team: Comet ISON's dust tail could wrap around Earth twice, then some
  • It is expected to pass within sun's atmosphere, and it should put on a big show
  • Experts: Comet won't threaten Earth, even if sun's heat breaks it apart as it passes

Comet ISON may put on a show when it skims through the sun's atmosphere later this year. Right now, it's still far away, but we're keeping track and will give you regular updates. Here are five key facts about ISON as we await its arrival:

What's with the funky name?

Comet ISON was discovered by Russian astronomers Vitali Nevski and Artyom Novichonok in September 2012. It's named after their night-sky survey program, the International Scientific Optical Network, a group of observatories in 10 countries organized to track objects in space.

How big is it?

Measurements taken by the Hubble Space Telescope in April indicate ISON has a nucleus that is 3 to 4 miles across. The comet's head, or coma, is estimated to be 3,100 miles across, or 1.2 times the width of Australia. The Hubble team says its dust tail extends more than 57,000 miles -- more than twice the circumference of Earth, and far beyond the telescope's field of view.

OK, it's a comet. Aren't there lots of comets? Why is this one special?

Some early comet prognosticators have tagged ISON "the comet of the century."

"Comet ISON has the potential to be among the brightest comets of the last 50 years," Dennis Bodewits, an astronomer at University of Maryland at College Park, told NASA.

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Bodewits and other astronomers used NASA's Swift satellite to estimate ISON's water and dust production.

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"Comet ISON belongs to a class of comets called Sungrazing comets," Karl Battams of the Naval Research Lab told CNN. This means it will fly relatively close to our sun. These comets "teach us not only about comets, but also yield valuable and unique results about the sun," he said.

But before you get too excited, other experts caution it's too early to know what ISON will do.

"Predicting the behavior of comets is like predicting the behavior of cats -- can't really be done," Don Yeomans of NASA's Near-Earth Object Program told CNN.com in March.

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When can I see it?

In November, ISON is expected to fly through the sun's atmosphere at about 700,000 miles above the surface. If it survives the sun's heat, experts say it might glow as brightly as the moon and be briefly visible in daylight. Its tail might stretch far across the night sky. Or the sun could cause it to break apart.

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What if ISON breaks apart? Is Earth in danger?

No. Experts say the comet won't threaten Earth. In fact, even if it breaks up, Battams says it could put on a big show.

"If Comet ISON splits, it might appear as a 'string of pearls' when viewed through a telescope," Battams told NASA. "It might even resemble the famous Comet Shoemaker-Levy 9 that hit Jupiter in 1994."

Whatever happens to ISON, sky watchers in the Northern Hemisphere should have a good view for several months. NASA says it will pass almost directly over the North Pole and will be visible all night long.

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