Characteristics of the Moon

Here are the key characteristics of the Moon, Earth’s only natural satellite:

Basic Facts

• Diameter: About 3,474 km (roughly 1/4 the size of Earth)

• Distance from Earth: ~384,400 km on average

• Gravity: 1/6th of Earth's gravity

• Orbital Period: About 27.3 days (sidereal), 29.5 days (synodic or full moon to full moon)

Physical Features

• Surface: Rocky, dusty, and covered in fine gray regolith (powdery soil from micrometeorite impacts)

• Craters: Heavily cratered from billions of years of impacts

• Maria (plural of Mare): Large, dark basaltic plains formed by ancient volcanic activity

• Highlands: Bright, rugged regions with older terrain than the maria

Environment

• Atmosphere: Extremely thin exosphere, nearly a vacuum

• Temperature Range:

  • Daytime: Up to 127°C (260°F)

  • Nighttime: Down to -173°C (-280°F)

• No Weather: No wind, rain, or erosion (except from impacts)

Motion and Behavior

• Synchronous Rotation: The Moon always shows the same face to Earth (its rotation period equals its orbit period)

• Phases: Caused by its position relative to the Sun and Earth

• Eclipses:

  • Solar Eclipse: Moon passes between Earth and Sun

  • Lunar Eclipse: Earth passes between the Sun and Moon

Interesting Traits

• No Liquid Water: But ice exists in permanently shadowed craters at the poles

• Seismic Activity: Known as “moonquakes,” some caused by tidal forces from Earth

• Formation Theory: Believed to have formed from debris after a Mars-sized body collided with Earth ~4.5 billion years ago