The Coathanger Asterism

asterism Jul 22, 2023

The Coathanger asterism within Vulpecula the Fox Constellation

The Coathanger, also known as Collinder 399 or Brocchi's Cluster, is a well-known and easily recognizable asterism in the night sky. An asterism is a prominent star pattern that is not officially recognized as a constellation. The Coathanger, in particular, is a distinctive and interesting group of stars.  

The Coathanger is located in the constellation Vulpecula, which is a small and faint constellation in the northern celestial hemisphere. Vulpecula means "little fox" in Latin. The Coathanger gets its name because it resembles the shape of a coat hanger or a hook. It is formed by a line of stars that appears to curve at one end, similar to the hook of a coat hanger. The Coathanger is composed of about 10 to 12 stars that are relatively bright and form this distinctive pattern.  It's important to note that the Coathanger is not a true star cluster, but rather a chance alignment of stars along our line of sight. The stars that make up the Coathanger asterism are not physically associated with each other; they are at different distances from Earth.

The Coathanger asterism is one of the few things or patterns in the night sky that actually looks like what its name says. The Coathanger asterism goes by not one but 3 different names. One of those names is Al Sufi's Cluster, named after the Persian astronomer Al Sufi who first described this celestial object in his book of fixed stars in 964. It also goes by the name Brocchi's Cluster and this was named after an American amateur astronomer Dalermo Brocchi. He was based in Seattle, and he created a map of this star cluster. He observed variable stars a lot and contributed a great deal to the field of astronomy. He did a lot of his work in the 1920s. For most of the 20th century it was thought that the stars within Brocchi’s cluster were gravitationally bound to each other, but recent measurements from the Hipparcos mission reveal that these stars are not grouped together in space.

Finding the Coathanger Asterism

The Coathanger asterism is one that can be seen with an unaided eye, but it's definitely best if you can seek out dark skies in order to find it. For a closer view of it you can use a pair of binoculars or a low-powered telescope. To identify the Coathanger Asterism in the night sky it can first be helpful to identify Aquilla in the night sky using the Summer triangle. Then hop over to Sagitta and identify the arrow shape. The Coathanger asterism should be in close proximity to Sagitta. Another strategy for finding the Coathanger Asterism is drawing an imaginary line from Vega, down to Altair. The Coathanger asterism should be located along the imaginary pathway.

The stars that make up the Coathanger asterism are all relatively bright and visible to the naked eye under good observing conditions. They vary in magnitude but are generally around the 6th to 7th magnitude range. The Coathanger is best observed during the summer months in the northern hemisphere when the constellation Vulpecula is well-placed in the night sky. It can be spotted using binoculars or a small telescope, and it's a popular target for amateur astronomers.