sky chart showing comet Lulin
Sky chart showing comet Lulin on Feb. 24, 2009. Image credit: NASA/JPL
We hear a lot about "going green" these days. The latest to join in the trend is comet Lulin, which is making an appearance in the nighttime sky this month. Don Yeomans of JPL, manager for NASA's Near-Earth Object Program Office, answers a few questions about this odd comet.

Q: Why is comet Lulin green?
A: The ices in comet Lulin vaporize into gases when its nucleus gets close enough to the sun. These gases appear greenish due to the emission of carbon (C2) and the lack of a significant yellowish dust tail that sometimes dominates the color of an active comet.

Q: What other unusual characteristics does the comet have?
A: Comet Lulin is moving nearly in the same orbital plane around the sun as do the planets, but in the opposite (retrograde) direction. It is probably the first time this comet has entered the inner solar system, so some of its original volatile ices in its nucleus may still be present, and should be identifiable during observations.

Q: Will we be able to see comet Lulin and its greenish color? If so, where, when and how?
A: The comet should be observable in dark skies with binoculars. The best time to observe might be near its closest approach to Earth (about 38 million miles) on Tues., Feb. 24, when the comet appears just below the planet Saturn in the constellation of Leo (high in the southeast in late evening for observers in mid- northern latitudes, for example, in the United States and Europe.

Q: Will NASA astronomers be tracking the comet?
A: A small army of amateur and professional astronomers will certainly take advantage of this young comet using various telescopes and in many different wavelengths. It is not that often that a relatively bright, young comet is seen in the inner solar system, and astronomers will take advantage of this opportunity to identify some of the gases that make up its greenish atmosphere - and infer what exotic ices make up its unseen nucleus.