Astronomy: Meet ISON, the unknown comet

3:16 AM, Oct 28, 2013   |    comments
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( - This comet doesn't have a cool name like Kohoutek, Hale-Bopp or the Great Daylight Comet of 1910 - in fact, Comet ISON's name is an acronym for the International Scientific Optical Network.

But soon after Russian astronomers Vitali Nevski and Artyom Novichonok discovered Comet ISON in September 2012, many in the astronomy community predicted it would put on a spectacular naked-eye show for the Northern Hemisphere in November and December 2013, possibly becoming as bright as the full moon and visible during the day; some media outlets started calling ISON The Comet of the Century and The Great Comet of 2013.

ISON can now be seen with small telescopes and might soon be visible through good binoculars, but in recent months, sky watchers are a little less certain about the comet's upcoming performance.

"We don't know for sure what it will do," said Carole Holmberg, planetarium director at the Calusa Nature Center and Planetarium. "The initial predictions were that it would be extraordinary. But it hasn't lived up to the hype. But it still has the potential to be the comet of the century."

One reason expectations were so high for Comet ISON is that this is its first trip around the sun.

Comets can come from one of two locations, the Oort Cloud, which is a swarm of ice chunks beyond Pluto, and the Kuiper Belt, another cloud of ice chunks beyond the orbit of Neptune.

Every now and then, an ice chunk is bumped out of its orbit by the gravity of a passing star, planet or molecular cloud, and it falls into the gravitational pull of the sun - a comet is born.

As the comet approaches the inner solar system, the sun's radiation vaporizes some of the frozen material, known as volatiles; the vaporized material forms an envelope, the coma, that surrounds the comet.

Solar wind and radiation pressure blow part of the coma away from the comet to form a tail; think of a strong wind blowing Willie Nelson's hair back (the word "comet" is from the Greek "aster kometes," meaning "long-haired star").

Every time a comet orbits the sun, it loses some of its volatiles; because this is ISON's first trip, it still has its volatiles, which means there is plenty of stuff to vaporize and form a tail.

On Oct. 1, ISON passed within 6.5 million miles of Mars and will zip around the sun at 845,000 mph on Nov. 28, Thanksgiving Day, to begin its outbound journey.

ISON is what astronomers call a "sungrazer," because it will pass through the sun's atmosphere, and that could be a problem: Tidal forces and temperatures of more than 1 million degrees might simply destroy the comet.

On the other hand, Comet Lovejoy flew into the sun's atmosphere in December 2011 and came out on the other side to wow the Southern Hemisphere with a tail that extended across half the sky.

"I can imagine three scenarios," Holmberg said. "One, it will evaporate, and there will be nothing left. Second, it could break up; you'd think that would be great, but without a single nucleus, there will be nothing bright to look at.

"Third, it will round the sun intact and be just spectacular. My opinion is that there's less than a 50-percent chance of that happening. That's not a scholarly opinion; it's more a gut feeling."

Michael Fauerbach, professor of physics and astronomy at FGCU, is equally unsure about what ISON will do.

"Unfortunately, my prediction is going to be as expert as yours: Comets are incredibly hard to predict how they'll behave," he said. "So far, it's been more of a disappointment. People thought it would be brighter than it is. As it gets closer to the sun, it might break up, which would be great for telescopes but not for a sky show.

"I have a feeling it won't be the comet of the century."

Comet ISON is now near Mars and the 1.36-magnitude star Regulus in the constellation Leo, which rises in the eastern sky before dawn.

When it leaves Leo, the comet will pass through Virgo and Scorpio before its Thanksgiving date with the sun.

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