Page:The Music of the Spheres.djvu/263

 clearly seen, they would show phases like the moon. When in 1610, Galileo turned his telescope on Venus and beheld the beautiful little crescent, the followers of the ancient system of Ptolemy—who claimed that the earth was the central body around which the sun and planets revolved—were, for the first time, silenced, for they saw that the orbit of the earth must enclose the orbit of Venus, and that they must both revolve around the sun. Even a small telescope will show the phases of Venus, the crescent being far more beautiful than one would imagine.

When first seen through a telescope, in the evening twilight, Venus is gibbous, or nearly round. It has then just emerged on the farther side of the sun from us. After first becoming visible as a disk, it gradually assumes the figure of a half moon (this is at the point of its greatest elongation when it is at its highest in the sky); then as it again approaches the sun, it gradually becomes more and more like a slender crescent of light. When Venus is showing nearly a full face, it is the whole diameter of its orbit farther away than when it shows a slender crescent. In this position it is 160 millions of miles distant from the earth; when nearest the earth it is only 22 millions of miles distant. This is the reason why it appears much smaller when its full hemisphere is turned toward us than when it is seen as a small crescent. The proportion of this disk to the crescent is as 10 to 65. After becoming a "silver bow," Venus disappears from the evening sky, later to appear on the other side of the sun in the