Origins -- According to the leading theory, the moon was created when a rock the size of Mars slammed into Earth about 4.5 billion years ago.
Moon craters -- The moon's heavily cratered surface is the result of intense pummeling by space rocks between 4.1 billion and 3.8 billion years ago.
Locked in orbit -- Long ago, the Earth's gravity slowed the moon's rotation around its axis. The result? We only see one side of the moon at all times.
Egghead -- The moon is not round, or even spherical. Instead, it's shaped like an egg.
Moon trees -- Did you know more than 400 trees on Earth came from the moon? Well their seeds orbited around the moon with Apollo 14 astronaut Stuart Rosa, who took a bunch of seeds with him on a moon mission in 1971.
Planet moon? -- At roughly one-fourth the diameter of Earth, some scientists think the moon is more like a planet and refer to the earth-moon system as a "double planet."
Sister moons -- In 1999, scientists found a 3-mile-wide asteroid that may be caught in Earth's gravitational field, thereby becoming a sister moon of sorts. Cruithne takes 770 years to complete its horseshoe-shaped orbit around Earth, and will remain in a suspended state around Earth for at least 5,000 years.
Bye-bye, moon -- The moon is slowly moving away from us. Each year, the moon steals some of Earth's rotational energy, and uses it to propel itself about 3.8 centimeters higher in its orbit.
Moonquakes -- The gray orb isn't a dead planet. Small moonquakes, originating several miles below the surface, are thought to be caused by the gravitational pull of Earth.
Ocean tug -- We all know the Earth's tides are caused mostly by the moon. But here's how it works. High tide aligns with the moon as Earth spins underneath. Another high tide occurs on the opposite side of the planet because gravity pulls Earth toward the moon more than it pulls the water.
Douglas MacArthur returns to the Philippines, Nixon sets off the "Saturday Night Massacre," Jackie Kennedy remarries, the Sydney Opera House opens, tragedy strikes Lynyrd Skynyrd, and Muammar Gaddafi is killed, all on this day.