Glenn Chaple's Observing Basics: A double take

January 2011: Spend an autumn evening getting reacquainted with the Double Cluster.

Contributed by Glenn Chaple

Published: November 19, 2010

The Double Cluster (NGC 869, right, and NGC 884) in Perseus is one of the heaven's most beautiful deep-sky objects. Each member spans slightly less than 1/2° and contains more than 100 stars.

Photo by Richard Jacobs

Gaze northeastward an hour or two after sunset on a late autumn evening from a dark site and you’ll likely notice an elongated smudge of light midway between Cassiopeia and the “head” of Perseus. More than 2 millennia ago, it caught the eye of the Greek astronomer Hipparchus, who referred to it as a “cloudy spot.” Thanks to the telescope, we now know that this smudge of light is in fact a dazzling pair of starry aggregations we call the Perseus Double Cluster.

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