Sky watch: Hop stars to find the Double Star Cluster

If you're outside just after dark on the week beginning Nov. 8, aim binoculars along the Milky Way low in the northeastern sky. About midway between the constellations Cassiopeia and Perseus, you may think you're seeing double.

And you are.

You're looking in the direction of the famous Double Star Cluster of Perseus, one of - or should I say two of - the most beautiful showpieces in the heavens. Under a clear sky, you might see the pair with the unaided eye as a single fuzzy patch of light.

Prehistoric stargazers almost certainly spotted this object but didn't know what it was. Not until around 150 BC did stargazers officially catalog it. The ancient astronomers Hipparchus and Ptolemy wrote about the pair, but they referred to it only as a "nebula" or "cloudy spot," one of the half-dozen or so they knew at the time.

Modern astronomers identify the Double Cluster as "h and chi Persei," as well as by the catalog numbers NGC 869 and NGC 884. The easternmost of the pair (NGC 884) is slightly larger but contains fewer stars - about 150 or so - while NGC 869 is physically smaller but contains about 200 stars.

At a distance of about 7,500 light years, these two clusters lie within only a few hundred light years of each other. They seem relatively young, most likely less than 13 million years old, and travel through space tethered by gravitation.

If you're unable to find the Double Cluster right away, try this "star hopping" technique to help you out.

First, find the constellation Cassiopeia. Or you'll probably have more luck finding a number 3 outlined by its five brightest stars now standing nearly vertically in the northeast during early evening hours. Simply trace its two nearly vertical stars, and extend that line downward about the same distance.

Aim binoculars or a small telescope in this direction, and you'll soon be rewarded with a double cosmic treat!