Sky Show This Month: Little Green Comet Nears Earth

Updated April 13, 2009

Amateur astronomers in South Korea and the U.S. have jointly discovered a faint new comet streaking across our solar system.

Called Yi-SWAN, the newfound comet is already visible to backyard telescopes in the Northern Hemisphere.

Sky-watchers will be able to see Yi-SWAN until about mid-May, when it will wander too close to the sun to be visible except to the largest telescopes.

The comet is named after Korean amateur astronomer Dae-am Yi, who first noticed it on March 26, and the SWAN instrument on board NASA's sun-gazing satellite SOHO.

(Related photo: "Sun Probe Spies New Periodic Comet.")

Meanwhile, amateur astronomer Rob Matson of California independently spotted the comet in publicly available SWAN images and notified the Central Bureau for Astronomical Telegrams (CBAT), the world clearinghouse for comet discoveries, on April 4.

The comet has since been seen by several astronomers around the world.

Yi-SWAN is traveling in a tilted elliptical orbit and is currently about 164 million miles (264 million kilometers) from Earth.

It is still too early to tell if Yi-SWAN will be a recurring visitor like Halley's comet, said CBAT director emeritus Brian Marsden.

"We'll need observations over several months before we'll be able to say that."

Crossing Cassiopeia

During its visit, Yi-SWAN will appear as a small, fuzzy dot in the sky. It's reported to have a faint greenish glow, or coma, around its main body.

No tail has been observed yet, but that may change as the comet moves closer to the sun.

In mid-April comet hunters should look near the constellation Cassiopeia to see Yi-SWAN.

The comet should be visible all night, although the best times to look are around dawn and dusk, when Cassiopeia is high in the sky. Around April 20, Yi-SWAN will move into the constellation Perseus.

Marsden cautioned that finding the comet could be challenging for novice astronomers.

"If you don't really know how to find locations in the sky, you will have trouble finding it," he said.

Dan Green, the current CBAT director, has these three suggestions for beginners:

Buy an introductory astronomy book and learn how to find an object's ascension and declination, the celestial versions of longitude and latitude. Then visit the CBAT Web site to get the comet's coordinates.

Contact a local planetarium or astronomy club and ask someone to point out the comet.

If all else fails, Green quipped, find a brighter comet to look at.

SOURCES AND RELATED WEB SITES

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