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of the backdrop stars. The moon's diameter equals about 1/2 degree, and your fist held at an arm length from your eye spans roughly 10o of sky. The moon's motion from night to night is due to its actual motion in orbit around Earth. Although the Earth's rotation causes the moon and stars to drift westward across the sky throughout the night, the moon's orbital motion continually propels the moon eastward through the stars over the course of each month.
• Bottom line: Watch the moon tonight (April 23, 2013) and in the next few nights. The moon can guide your eye to the star Spica and the planet Saturn, which is now out from nightfall till dawn.
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