Among the double stars, Young mentions an orange and blue, and a white and emerald green; the Rev. T. W. Webb points out one almost appetizingly attractive in its light apple green and cherry red while Serviss notes some charming combinations—orange and green, pale green and purple, light yellow and pale red—which may be seen with such meager assistance as an opera-glass. Serviss, by the way, has written a whole book on what may be seen in the sky with no greater aid than an opera-glass.
The star cluster in Hercules lies on the west side of the constellation, about one-third of the distance from the north end and not far from the figure of the Northern Crown. To the unaided eye, this cluster looks no more than a glimmering speck of light, but if a powerful telescope is trained upon it, it is resolved into a great cluster of stars. These stars, numbering into the thousands, are so packed together toward the center that they have been described as resembling "ice crystals in a snowball." From such a lovely blaze within the center another observer adds that "sprays of stars reach out in all directions like tendrils of a vine."
The stars counted on a photograph of the Hercules cluster which was taken by the great 60-inch reflector on Mount Wilson, number over 50,000! This telescope resolves even the solid glow of light at the center of the cluster into individual stars.
Sir Robert Ball in "Star-land" gives a good illustration of the appearance of a globular cluster of stars as seen in a large telescope. "I take a pepper-castor and on a sheet of white paper I begin to shake out pepper until there is a little heap in the center and the other grains of pepper are scattered loosely about. Imagine that every one of those grains of pepper was to be transformed into a tiny electric light, and then you would have some idea of what a cluster of stars would look like when viewed through a telescope of sufficient power."
A STAR CLUSTER IN HERCULES.
Photograph by Yerkes Observatory through 24-inch telescope. A photograph of the same star-cluster by the Mount Wilson Observatory through a 60-inch reflecting telescope is shown on page 2.
It was at one time thought that the cluster of Hercules might be a comparatively close cluster of small-sized suns, but Professor Shapley has lately discovered that the cluster is a very distant one; indeed it lies at such an exceedingly remote position in the realms of space that its parallax is slightly inferior to a 10,000th second of arc which corresponds to a little more than 36,000 light years. Thus it takes 36,000 light years for its light to reach us, for this light has to cross the unthinkable space of 220,000 billion miles!
LYRA, THE HARP