Descriptions of the Coma Cluster of galaxies sound like bad car-dealership commercials. The cluster contains more than a thousand galaxies. They’re bound together by their mutual gravitational pull. The heart of the cluster is about 330 million light-years away. But the cluster may span as much as two hundred million light-years.

But wait — that’s not all! There’s a lot more to the cluster than we can see. In 1933, Fritz Zwicky found that galaxies in the cluster are moving fast — too fast for the cluster to be held together by the gravity of the visible matter. He concluded that most of the cluster must consist of dark matter — matter that produces no energy, but pulls on the visible matter around it. Today, astronomers calculate that dark matter must make up at least 90 percent of the cluster’s mass.

But wait! We’re not through yet! More galaxies are falling into the Coma Cluster. One group is led by the giant galaxy NGC 4839. Gas is being stripped from the group. It forms a hot tail that’s a million-and-a-half light-years long. The group may have plunged through the cluster once, and now is making a second pass.

But wait! Oh, well — that’s all we have time for! We’ll just give you the cluster’s address. It’s in Coma Berenices. The constellation climbs into good view, in the east, by 8 or 9 o’clock. Some of its brighter stars form sparkling ribbons — with a cluster of galaxies far beyond.

Script by Damond Benningfield