moon: Solar and Lunar Eclipses

Although an optical illusion causes the moon to appear larger when it is near the horizon than when it is near the zenith, the true angular size of the moon's diameter is about 1⁄2°, which also happens to be the sun's apparent diameter. This coincidence makes possible total eclipses of the sun in which the solar disk is exactly covered by the disk of the moon. An eclipse of the moon occurs when the earth's shadow falls onto the moon, temporarily blocking the sunlight that causes the moon to shine. Eclipses can occur only when the moon, sun, and earth are arranged along a straight line—lunar eclipses at full moon and solar eclipses at new moon.

Sections in this article:

• Introduction
• Formation and Evolution
• Internal Structure
• Surface Features
• Physical Characteristics
• Tidal Influence of the Moon
• Solar and Lunar Eclipses
• Retarded Lunar Motion
• The Lunar Orbit and Phases
• The Lunar Month
• The Earth-Moon System
• Bibliography

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