Seeing Double in Perseus

By Dennis Mammana

October 4, 2018 4 min read

Week of Oct. 7-13, 2018

We astronomers call them "faint fuzzies," and if you have a good dark sky away from city light pollution, you'll soon find that they're sprinkled all over the heavens. This odd moniker originates from the appearance of the objects: faint, fuzzy smudges to which most beginning stargazers pay little attention.

But spend some time under a dark sky with binoculars or a small telescope and you'll soon understand why astronomers love the faint fuzzies. Many appear in the sky during late summer and early-autumn evenings, but one of my favorites lies midway between the constellations Cassiopeia and Perseus low in the northeastern sky after dark this week.

Aim binoculars or a small telescope in this direction and you may think you're seeing double. That's because you are.

This is the celestial home of one of — or, should I say two of — the most beautiful faint fuzzies in the heavens. Under a clear, dark sky, you might even be able to see the pair with the unaided eye as a single softly glowing wisp of light.

Prehistoric sky watchers almost certainly spotted this object but, of course, had no idea what it was. It wasn't until around 150 B.C. that stargazers officially noted it in their catalogs. The ancient astronomers Hipparchus and Ptolemy 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 it as "h and chi Persei," as well as by the catalog numbers NGC 869 and NGC 884; most of us, however, know it simply as the Double Cluster of Perseus. The easternmost of the pair, NGC 884, is slightly larger but contains fewer stars — about 150 or so — while NGC 869 is physically smaller and contains about 200 stars.

At a distance of some 7,500 light-years, these two star clusters lie within only a few hundred light-years of each other — pretty close by cosmic standards. They also seem to be relatively young — most likely less than 13 million years old — and travel through the galaxy 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. This star grouping represented to the ancients a lovely queen who was so smitten by her own beauty that when the gods placed her among the stars, they positioned her so she'd spend half of her time upside down. If you watch her over an entire night — or through an entire year — you'll easily understand the origin of this idea.

Now, you can certainly search for a celestial queen if you like, but you'll probably have more luck finding the letter "W" 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 as their separation.

Look carefully and you may see this wonderful object with your own eyes, but aim binoculars or a small telescope in its direction and you'll soon be rewarded with a double cosmic treat!

 See double in Perseus after dark this week.
See double in Perseus after dark this week.

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