This comet won't be round for another 8,000 years, so why is it green?

A glowing green comet is making its closest approach to Earth and providing amateur astronomers with a once-in-a-lifetime opportunity that will not come again for 8,000 years.

On a clear dark night, Comet Lovejoy is just about bright enough to be glimpsed as a small smudge of light with the naked eye.