#collinder 399

Brocchi's Cluster is not a true star cluster. Instead it is an asterism, just a collection of stars on the sky that look close together but are actually hundreds of light years apart.

Brocchi's Cluster, also known as the Coathanger // Dieter Willasch

Brocchi's Cluster (above right of center) // Alex Woronow

This is not actually a cluster of stars, as all of them lie at different distances from Earth. This is just a chance alignment!

Brocchi’s Cluster, also known as the Coathanger // AC1000

Is this coat hanger a star cluster or an asterism? This cosmic hang-up has been debated over much of last century, as astronomers wondered whether this binocular-visible object is really a physically associated open cluster or a chance projection. Chance star projections are known as asterisms, an example of which is the popular Big Dipper. Recent precise measurements from different vantage points in the Earth's orbit around the Sun have uncovered discrepant angular shifts indicating that the Coat Hanger is better described as an asterism. Known more formally as Collinder 399, this bright stellar grouping is wider than the full moon and lies in the constellation of the Fox (Vulpecula).