"Comet Pojmanski (C/2006 A1) has a bright green head," says Chris Schur who took this picture yesterday at dawn from Payson, Arizona.

What makes a comet green? The atmosphere of the comet--called "the coma"--contains cyanogen (CN), a poisonous gas, and diatomic carbon (C2). Both of these substances glow green when illuminated by sunlight.

See for yourself. Comet Pojmanski (5th magnitude) is an easy target for backyard telescopes. Look for it left of Venus in the early morning sky: MAP