[Illustration: THE GREAT HERCULES CLUSTER--A UNIVERSE OF SUNS Taken with 60-inch Reflector of the Mt. Wilson Observatory]
The constellation of Hercules is a very rich field for the possessor of even a small telescope. Here are to be found beautifully colored double stars in profusion, and, in addition, two remarkable clusters of stars. The brighter of the two is known as the Great Hercules Cluster. Its position is shown on the chart, and, under favorable conditions--that is, on a clear, dark night, when there is no moonlight--it may be seen without the aid of a telescope as a small, faint patch of light. One would never suspect from such a view what a wonderful object this cluster becomes when seen with the aid of a powerful telescope. Photographs taken with the great telescopes show this faint wisp of light as a magnificent assemblage of thousands of stars, each a sun many times more brilliant than our own sun. The crowded appearance of the stars in the cluster is due partly to the fact that it is very distant from the earth, though neighboring stars in the cluster are indeed much nearer to one another than are the stars in the vicinity of our solar system. It has been found that this cluster is so far away that its light takes over thirty-six thousand years to reach the earth. At the distance of this cluster, a sun equal in brightness to our own sun would be so faint that the most powerful telescope in the world would not show it. So we know that the stars that are visible in the Hercules cluster are far more brilliant than our sun. A fair-sized telescope will show about four thousand stars in this cluster, but the greatest telescopes show over one hundred thousand in it, and there are without doubt many more too faint to be seen at all. The Hercules cluster is called a globular star-cluster, because the stars in it are arranged nearly in the form of a sphere. There are in the heavens about ninety such clusters whose distances have been found, and they are among the most distant of all objects. Most of them are very faint, and a few are over two hundred thousand light-years distant from the earth. The Hercules cluster is one of the nearest and is the most noted of all of these globular clusters. It is considered to be one of the finest objects in the heavens. The other cluster in Hercules is also very fine, but not to be compared with this one.