Pictures of open star clusters
A guide to open star clusters and images captured by astrophotographers.
An open star cluster is a young group of loosely bound stars that all formed from the same vast region of cosmic gas known as a giant molecular cloud.
Open clusters contain just hundreds or a few thousand stars gravitationally bound, but because they are loosely bound the stars spread out from one another over time. This is why they are known as ‘open’ star clusters.
This weakness in gravitational attraction between the stars in an open cluster is what makes gives them such irregular shapes.
Open star clusters are are also young, at just tens or hundreds of millions of years old.
Open clusters vs globular clusters
Open star clusters can be easily contrasted with globular clusters, because their properties are almost the mirror opposite of one another.
- Open star clusters are loosely-packed, containing hundreds or thousands of stars
- Globular clusters are densely packed, containing hundreds of thousands or even millions of stars.
- Open star clusters form loose, irregular shapes
- Globular clusters form dense, consistently round shapes
- Open star clusters are tens or hundreds of millions of years old
- Globular clusters are some of the oldest objects in the Universe: even as old as 12 billion years
There are thousands of open star clusters in the Milky Way, and they can be found in the disc of our Galaxy.
While the individual stars in an open cluster may last for billions of years, the cluster itself won’t last as long, because the lack of strong gravitational attraction causes them to disperse over time.
Open star clusters are extremely beautiful objects to observe and to photograph. Below is a selection of images of open clusters captured by BBC Sky at Night Magazine readers and astrophotographers.