This photograph captures Comet 17P/Holmes as it moves across the Alpha Persei stellar association (Melotte 20). Comet Holmes underwent an enormous, unexpected outburst on October 25, 2007, becoming over half a million times brighter over the course of a just a few hours. Nearly 4 weeks later when this photograph was taken, its coma had grown larger than the sun.
This shot is a combination of 3 7-minute exposures stacked to average out sensor noise. The camera was piggy-backed on an motor-driven equatorial mount to track and cancel out star trailing during the long exposures.
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