Charles Messier was a comet hunter. But he kept coming across annoying objects that resembled comets. So he compiled a catalog of them to keep both himself and others from wasting time – more than a hundred in all. And 250 years ago tonight, while studying a comet in Cassiopeia, he discovered object number 52 – a star cluster that’s thousands of light-years from Earth.

Astronomers have been studying Messier 52 ever since then. Yet they still don’t know all of its details. That includes its precise distance. Measurements made in recent years have ranged from less than 5,000 light-years to more than six thousand. And without knowing the cluster’s distance, it’s hard to nail down its other characteristics. Its age, for example, could range from 120 million to 160 million years.

A study a few years ago counted 369 stars in the cluster, although the total’s probably much higher. Many of the stars are crowded in its middle. But some of them are dozens of light-years from there. At the cluster’s edge, stars can be pulled away by the gravity of the rest of the galaxy – reducing the size of this family of stars.

M52 is well up in the northeast at nightfall. It’s above the sideways letter W formed by some of Cassiopeia’s brighter stars. The cluster is too faint to see with the eye alone, but it’s an easy target for binoculars.

Tomorrow: A ruby jewel atop a stellar diamond.

Script by Damond Benningfield