The Moon is Earth's only permanent natural satellite and the brightest celestial object in the night sky after the Sun. It is a large, rocky body that orbits Earth, reflecting light from the Sun.

Key Characteristics

• Formation: The most widely accepted theory is that the Moon formed about 4.5 billion years ago from the debris of a massive collision between the early Earth and a Mars-sized object named Theia.
• Size and Mass: The Moon's diameter is about 3,476 kilometers (2,160 miles), which is roughly one-quarter the size of Earth. Its mass is about 1/81 of Earth's, resulting in a surface gravity that is only one-sixth of Earth's gravity.
• Orbit and Rotation: It takes approximately 27.3 Earth days for the Moon to complete one orbit around Earth and one rotation on its axis. This synchronous rotation means the same side of the Moon (the near side) always faces Earth.
• Surface: The lunar surface is airless and pockmarked with thousands of impact craters, mountains, and large, dark, flat plains called maria (Latin for "seas"). These maria were formed by ancient volcanic lava flows that filled impact basins billions of years ago. The surface is covered in a layer of fine, grey dust and broken rock called regolith.
• Atmosphere: The Moon has a very thin and weak atmosphere, more accurately described as an exosphere, so it has no weather or wind to cause erosion.
• Temperature Extremes: Without a thick atmosphere to regulate temperature, the Moon experiences extreme conditions. Temperatures can reach about 127°C (260°F) in direct sunlight and plummet to around -173°C (-280°F) in the shade.
• Water: Water ice has been confirmed to exist in permanently shadowed craters, particularly near the lunar poles, where temperatures are extremely low.
• Influence on Earth: The Moon's gravitational pull is the primary cause of Earth's ocean tides.