The comet makes its closest approach to Earth (0.41 AU) February 24, 2009. Current estimates peg the maximum brightness at 4th or 5th magnitude, which means dark country skies would be required to see it. No one can say for sure, however, because this appears to be Lulin's first visit to the inner solar system and its first exposure to intense sunlight. Surprises are possible.
Lulin's green color comes from the gases that make up its Jupiter-sized atmosphere. Jets spewing from the comet's nucleus contain cyanogen (CN - a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight in the near-vacuum of space.
The comet will rise a few hours before the Sun, maybe 3am, in the southern sky. February 16th and 24th will be the best days, but no one really knows how bright Lulin will be since it's never passed this way before.
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