Ken Sabourin, age 9, of Ottawa, Ontario, Canada, for his question:

What are star clusters?

There are zillions of stars and some of them cluster together in clumps. An open cluster may have 100 or so stars that are fairly close together. Our Big Dipper belongs to an open cluster. But it is fairly close to us and we do not notice its group of relatives. There are hundreds of open star clusters in our sky, but most of them are too far away for our eyes to see.

Then there are other groups called globular clusters. Some look like single stars because they are so far away. In the telescope, we see that a globular cluster looks like a swarm of golden bees. Actually, it is perhaps 50,000 bright stars, crowded rather closely together in a round ball. Astronomers have spotted many of these bright starry clusters near the center of the Milky Way.