Open Clusters

Stars may sometimes be grouped in numbers of the 100s or the 1000s. Typically, stars that formed in the same nebula and generally stuck together are loosely bound to each other in what is called an open cluster.


An open cluster is just as it sounds. The cluster of stars does not have a defined shaped but does have defined members. These are the characteristics of pen clusters.

• Open clusters consist of younger stars (i.e. bluer stars) with higher metallicities.
• Typically, we find open clusters in the disk of our Milky Way because that is where the younger stars generally are found in our galaxy.
• Open clusters contain anywhere from a few dozen to a few hundred stars and are about 20 light-years across with the main body being about 3 to 4 light years in size.

Open clusters can easily be found in the night sky. In fact, if you look at the constellation Taurus, there is a really bright cluster above the head of Taurus called the Pleiades, or the Seven Sisters.

Pleiades Open Cluster

via APOD



Another example of a open cluster is actually found in the same constellation. The Hyades are found in the head of Taurus and are near the star Aldebaran. Though Aldebaran appears to be in the cluster, it is not because of its age, size, and distance from the others.

Hyades Open Cluster

via APOD

Next time, we will talk about a different stellar cluster, globular clusters.