Green Comet Approaches Earth

Green Comet Approaches Earth

02.04.2009

 

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Comet Lulin resources: ephemeris, 3D orbit, photo gallery

Discoverer’s Blog: Quanzhi Ye is following the comet across the night sky and blogging about his experiences in both English and Chinese: click here.

Comet Tails: Comet Lulin appears to have two tails. A quick lesson in comet anatomy explains why:

The green ball in the middle of Newton’s photo is the comet’s atmosphere or coma. It measures about 500,000 km across, more than three times wider than the planet Jupiter.

To the right of the coma is the comet’s ion tail. It is a wispy streamer of ionized gas pushed away from the comet by solar wind. The ion tail points almost directly away from the sun.

To the left of the coma is the comet’s dust tail. Like Hansel and Gretel leaving bread crumbs to mark their path through the forest, Comet Lulin is leaving a trail of comet dust as it moves through the solar system. Compared to the lightweight molecules in the ion tail, grains of comet dust are heavier and harder for solar wind to push around. The dust tends to stay where it is dropped. The dust tail therefore traces the comet’s curved orbit and does not point directly away from the sun as the ion tail does.

From a vantage point on Earth, much of the dust tail is hidden behind the coma, with only a little bit sticking out to the left. This creates the visual impression that the dust tail is pointing directly away from the ion tail and thus directly toward the sun. It is not, but it sure looks that way! The ion and dust tails are often called the "tail and anti-tail."

NASA’s Future: US Space Exploration Policy

 

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