Key Takeaways:
On some clear, moonless night this fall, head out and locate the constellation Vulpecula the Fox. It’s not the easiest star pattern to identify, but two much more apparent constellations will help you get into the right area. Vulpecula lies south of Cygnus and north of Aquila. And while you might be thinking, ah, he’s leading us to the Dumbbell Nebula (M27), actually our journey to the Fox is to find a sweet-looking asterism that’s usually called the Coathanger. Because it looks like a coathanger.
I say “usually” because it’s also designated as Collinder 399, Brocchi’s Cluster, and Al Sufi’s Cluster. And although it has a total integrated magnitude of 3.6, that brightness is spread out across a circle 1° in diameter. So, you’ll probably need binoculars to find it. Most finder scopes also can show you the entire figure.
The first person to record it was Persian astronomer Al Sufi (A.D. 903–986). He discovered this object and included it in his Book of Fixed Stars, which he published in the year 964.
American Dalmiro Francis Brocchi (1871–1955) also has his name attached to the Coathanger. He was an amateur astronomer and chartmaker for the American Association of Variable Star Observers. In the 1920s, he created a map of this region with accurate star brightnesses so that astronomers could calibrate their photometers, devices that measured how much light they received from individual stars.
Finally, the Coathanger has the designation Collinder 399 (often written Cr 399) because it was the 399th entry (out of 471) in a catalog of open clusters compiled by Swedish astronomer Per Arne Collinder. Well, it might have been considered a star cluster in 1931, when Collinder published his catalog. Now astronomers know that the stars are not physically related, so they’re not a cluster. They just happen to be in the same area of sky.
To find this cool object, extend a line south from magnitude 3.0 Albireo (Beta Cygni) through magnitude 4.4 Alpha Vulpeculae. That distance is roughly 3°. Head 4½° farther south, and your field of view should encompass the Coathanger. Ten of its stars glow brighter than 7th magnitude. The brightest are 4 Vulpeculae at magnitude 5.1, 5 Vulpeculae, at magnitude 5.6, and 7 Vulpeculae, which shines at magnitude 6.3. These stars, and perhaps a few more (depending on your eyes) can be seen by observers without optical aid on dark nights.
I’m surprised at how few amateur astronomers have seen the Coathanger. At observing sessions, I’ve occasionally attached binoculars to a tripod and aimed it at this asterism, inviting everyone to come have a look. The people who see it for the first time are delighted. I think you will be, too, even if it is upside-down!
