The brightest and largest object in our night sky, the Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate. It also causes tides, creating a rhythm that has guided humans for thousands of years.
The Moon was likely formed after a Mars-sized body collided with Earth several billion years ago.
Earth's Moon is the only place beyond Earth where humans have set foot, so far.
Earth's only natural satellite is simply called "the Moon" because people didn't know other moons existed until Galileo Galilei discovered four moons orbiting Jupiter in 1610.
In Latin, the Moon is called Luna, which is the main adjective for all things Moon-related: lunar.
Size and Distance
With a radius of about 1,080 miles (1,740 kilometers), the Moon is less than a third of the width of Earth. If Earth were the size of a nickel, the Moon would be about as big as a coffee bean.
The Moon is an average of 238,855 miles (384,400 kilometers) away. That means 30 Earth-sized planets could fit in between Earth and the Moon.
The Moon is slowly moving away from Earth, getting about an inch farther away each year.
Water on the Moon
During the initial exploration of the Moon, and the analysis of all the returned samples from the Apollo and the Luna missions, we thought that the surface of the Moon was dry.
The first definitive discovery of water was made in 2008 by the Indian mission Chandrayaan-1, which detected hydroxyl molecules spread across the lunar surface and concentrated at the poles. Missions such as Lunar Prospector, LCROSS, and Lunar Reconnaissance Orbiter, have not only shown that the surface of the Moon has global hydration but there are actually high concentrations of ice water in the permanently shadowed regions of the lunar poles.
Scientists also found the lunar surface releases its water when the Moon is bombarded by micrometeoroids. The surface is protected by a layer, a few centimeters of dry soil that can only be breached by large micrometeoroids. When micrometeoroids impact the surface of the Moon, most of the material in the crater is vaporized. The shock wave carries enough energy to release the water that’s coating the grains of the soil. Most of that water is released into space.
In October 2020, NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) confirmed, for the first time, water on the sunlit surface of the Moon. This discovery indicates that water may be distributed across the lunar surface, and not limited to cold, shadowed places. SOFIA detected water molecules (H2O) in Clavius Crater, one of the largest craters visible from Earth, located in the Moon’s southern hemisphere.