Astronomers love star clusters. All the stars in a cluster were born at the same time, from the same cloud of gas and dust. So any differences in the stars are the result of their evolution, which is a result of their mass. That makes it easier to learn what’s going on inside the stars.

One problem, though, is identifying which stars belong to a cluster. It takes detailed measurements of motion and brightness to separate members of the cluster from stars that just happen to line up in the same direction.

An example is the Coma star cluster, in Coma Berenices. The constellation is in the east at nightfall. Under dark skies, the cluster is a good target for binoculars.

The cluster is about 280 light-years away. But it spans dozens of light-years, so its stars are spread out. That makes it harder to pick out its members. And it takes big telescopes to pick out its fainter stars.

So despite decades of study, astronomers are still locking down the census of stars in the Coma cluster. A study about a decade ago confirmed eight small, faint members – the first of their kind known to belong to the cluster. And another study found that about a quarter of the stars in the cluster are binary or multi-star systems.

These discoveries bring the total number of stars in the Coma cluster to several dozen, with a few dozen more possibilities – members of a wide-spread stellar family.

More about Coma Berenices tomorrow.

Script by Damond Benningfield