Page:The Music of the Spheres.djvu/328

 is exceptionally dark and flat and forms a striking contrast with the bright border of mountains which surround it. Quite a number of minute craterlets have been distinguished on its floor.

The southern hemisphere of the moon, particularly as one approaches the region about the southern pole, is pitted with such a bewildering number of both large and small craters that astronomers say that it is relief to the eye to study the comparatively smooth, shaded portions of the globe after having gazed for any length of time at the crowded mass of detail in this wild and rugged region. The two craters in the southern hemisphere that are perhaps the easiest for the amateur to locate are Clavius, an enormous crater near the mountains at the southern pole, and Tycho, just below it, with its wonderful streaks, or rays.

Clavius is a crater of gorgeous depth and has an area of 16,500 miles. Around its walls and on its floor are many secondary craters, while from its center rise tall mountain peaks, one of which reaches 24,000 feet above the bottom of one of its included craters.

Tycho is called "The Metropolitan Crater of the Moon," because its brilliant rays stand forth so prominently when the moon is full that all other craters are lost in obscurity. This magnificent crater measures 54 miles from rim to rim with its floor over 3 miles below the highest ridge of the massive mountains which surround it. These mountains are diversified by a series of terraces on their interior slopes while a peak 6000 feet in height rises in the center of its floor. The ray system of Tycho is wholly invisible at the time the sun rises or sets, which is the time when most of the objects on the moon are seen at their best. However when the sun has attained an altitude of 30 degrees, they mysteriously make their appearance, extending for hundreds and some even for several thousands of miles. These rays are never irregular because of interposed obstructions but stretch straight and true in a most