The moon is Earth's natural satellite, a large rocky sphere that orbits our planet about once every 27 days. Unlike stars, the moon doesn't produce its own light. Instead, it reflects sunlight, which is why it appears to glow in the night sky and why its appearance changes throughout the month. When the sun illuminates the full face of the moon facing Earth, we see a full moon. When the sun lights only a sliver, we see a crescent moon.

The moon's gravity pulls on Earth's oceans, helping create the tides that rise and fall each day. This same gravitational pull also keeps the moon in its orbit around Earth. Astronauts first walked on the moon in 1969, discovering a barren landscape covered in gray dust and craters formed by asteroid impacts over billions of years.

The word moon can also mean to daydream or move aimlessly, like when someone moons around the house on a lazy Saturday. People also use moon as a verb meaning to gaze at something with longing or admiration.