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Comet Lulin
Did you notice the green, fuzzy object tracking its way across the sky throughout late February, 2009? It was comet Lulin, with a magnitude of around the fifth or sixth degree. Its green color originates from ionized cyanogens and carbon gases which emit green wavelengths. The green object was discovered by Quanzhi Ye at the Lulin Observatory in Taiwan in 2007, and it is an unusual comet in several ways.
Firstly, the comet is traveling backwards! It orbits in the opposite direction from the planets as it travels along the ecliptic plane, suggesting that it has never previously been within the inner solar system. This motion accounts for its velocity as the comet moves speedily over the evening sky--it moves approximately five degrees each day.
Additionally, comet Lulin has two tails. Because Earth is in the comet's orbital plane we see a thin, dusty "antitail" that resembles a spike, in addition to the bright gas tail we usually associate with comets. The gas tail constantly points directly opposite the sun as the comet orbits, while the dust tail lags behind slightly. Both tails are rarely seen at the same time from Earth.
On February 24, Lulin made its closest approach to Earth at 0.41 AU, or 38 million miles away. The next night, the comet was at opposition, when it was at its brightest. As we enter into March, the green comet will quickly slow down and fade as it moves farther away from the sun. We will probably not see comet Lulin again for another thousand years.
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