Here are the key characteristics of the Moon, Earth’s only natural satellite:
Basic Facts
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Diameter: About 3,474 km (roughly 1/4 the size of Earth)
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Distance from Earth: ~384,400 km on average
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Gravity: 1/6th of Earth's gravity
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Orbital Period: About 27.3 days (sidereal), 29.5 days (synodic or full moon to full moon)
Physical Features
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Surface: Rocky, dusty, and covered in fine gray regolith (powdery soil from micrometeorite impacts)
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Craters: Heavily cratered from billions of years of impacts
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Maria (plural of Mare): Large, dark basaltic plains formed by ancient volcanic activity
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Highlands: Bright, rugged regions with older terrain than the maria
Environment
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Atmosphere: Extremely thin exosphere, nearly a vacuum
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Temperature Range:
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Daytime: Up to 127°C (260°F)
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Nighttime: Down to -173°C (-280°F)
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No Weather: No wind, rain, or erosion (except from impacts)
Motion and Behavior
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Synchronous Rotation: The Moon always shows the same face to Earth (its rotation period equals its orbit period)
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Phases: Caused by its position relative to the Sun and Earth
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Eclipses:
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Solar Eclipse: Moon passes between Earth and Sun
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Lunar Eclipse: Earth passes between the Sun and Moon
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Interesting Traits
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No Liquid Water: But ice exists in permanently shadowed craters at the poles
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Seismic Activity: Known as “moonquakes,” some caused by tidal forces from Earth
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Formation Theory: Believed to have formed from debris after a Mars-sized body collided with Earth ~4.5 billion years ago