Astronomy Picture of the Day

Explanation: Near its closest approach to planet Earth, comet SWAN (C/2006 M4) brightened unexpectedly earlier this week, becoming visible to naked-eye observers under dark night skies. Telescopic observers also noticed dramatic changes in the comet's colorful coma and tail, seen in this view recorded on October 25th. To make the picture, images totaling eight minutes in exposure time were stacked and centered on the comet as it moved relatively quickly against the background star field. The picture covers about 1 degree on the sky. Northern hemisphere observers should still find the comet an easy binocular target in the early evening, even though moonlight will increase the overall sky brightness in the next few days. Look toward the northwestern horizon and the constellation Hercules.