Sunday, November 11, 2007
If you haven't seen it yet, get out to see Comet Holmes tonight. The image above will help you find it if you know Cassiopeia, or you can check out this larger sky chart here to orient yourself with the horizon and more stars.
A comet's tail trails off away from the sun, blown by the solar wind - it has nothing to do with the direction the comet is moving - (see this animation to understand better). Our present comet/Earth/Sun alignment gives us a rare "head-on" view (a fuzzy circle), rather than the more familiar side view (the tail is behind the fuzzy spot we're seeing).
The excerpt below comes from this Sky and Telescope article...
...The comet remains as bright as ever to the naked eye, though its average surface brightness continues to drop as it enlarges. As of last night it was 14 arcminutes wide, or nearly ¼° — half the apparent diameter of the Moon. During this dark-of-the-Moon period (which will end around November 15th), seize whatever chance the weather allows to show family, friends, and strangers something memorable. This is how new amateur astronomers are born.