The Moon
The Moon is Earth’s only natural satellite and the most familiar object in our night sky. It is the fifth-largest moon in the solar system and has influenced human culture, calendars, and exploration for thousands of years. Up close, it is a dry, cratered world with no atmosphere or liquid water.
Our Moon formed roughly 4.5 billion years ago, likely after a Mars-sized body collided with the early Earth. The debris from that giant impact eventually coalesced to form the Moon. This shared history explains why the Moon’s composition is very similar to Earth’s mantle.
Surface and Features
The Moon’s surface is covered with thousands of impact craters, dark volcanic plains called maria, and bright highlands. The large, dark patches we see from Earth are ancient lava flows that filled giant impact basins billions of years ago. The lighter highlands are older, heavily cratered regions that have remained largely unchanged for eons.
Because the Moon has almost no atmosphere, there is no weather or erosion to soften its features. Footprints left by Apollo astronauts more than 50 years ago are still perfectly preserved on the surface today.
Key Facts About the Moon
Diameter: 2,159 miles (3,475 km) — about one-quarter the diameter of Earth
Mass: 0.012 times Earth’s mass
Average Distance from Earth: 238,855 miles (384,400 km)
Day Length: 27.3 Earth days (same as its orbital period around Earth)
Surface Temperature: 260°F (127°C) during the day to -280°F (-173°C) at night
Phases and Influence
The Moon goes through a complete cycle of phases every 29.5 days as it orbits Earth. These phases occur because we see different amounts of the sunlit side of the Moon from our perspective. The Moon’s gravity creates tides in Earth’s oceans, and its presence helps stabilize Earth’s axial tilt, which contributes to our relatively stable climate.
The Moon has been visited by humans only during NASA’s Apollo program between 1969 and 1972. Twelve astronauts walked on its surface and brought back 842 pounds of lunar rocks and soil for study. Since then, several robotic missions from multiple countries have returned to map the Moon in greater detail and search for resources such as water ice in permanently shadowed craters near the poles.
Today, the Moon serves as a stepping stone for future exploration. Its low gravity and lack of atmosphere make it an excellent location to test technologies for deeper space travel. Scientists continue to study the Moon to better understand the early history of the solar system and the violent impacts that shaped the inner planets.
From the familiar face we see in the night sky to the rugged terrain explored by astronauts, the Moon remains one of the most accessible and scientifically valuable objects in our solar system.