The Moon

On average, the moon is 238,750 miles (384,400 km) from Earth, or about 30 Earth widths away.b Most scientists believe the moon formed as a result of a “Giant Impact,” or “Giant Whack.” According to this theory, a Mars-sized planet struck a glancing blow to early Earth. The impact “splashed off” rocks and debris into space, forming a huge ring around Earth that later clumped together to form the moon.b Not all full moons are the same size. Their size varies depending on whether the moon is at its apogee (far away) or perigee (nearby). The moon is generally 14% bigger when at its perigee.d When the moon is at its apogee (farthest from Earth), the tides and weather tend to be more predictable. When the moon is at its perigee (closest to Earth), the increased gravitational pull can create larger tides and more unstable weather.d The moon has had a violent history. It underwent what scientists call a Late Heavy Bombardment (LHB) or “lunar cataclysm” period somewhere between three and four billion years ago. During this time, the moon (and, most likely, Earth) was bombarded with meteorites.h The moon is more egg-shaped than round The moon is not round—it is shaped like an egg.e The moon’s core is 2-4% of its mass, whereas Earth’s core is about 30% of its mass.b Moonquakes, which originate several miles below the moon’s surface, may be a result of Earth’s gravitational pull. Engineers say these quakes could become a factor if lunar bases are ever built on the moon.d When the moon formed 4.6 billion years ago, it was 14,000 miles (22,530 km) from Earth. Now it’s more than 280,000 miles (450,000 km) away. The moon looked three times larger when it was closer to Earth.d Because the moon has no atmosphere, its temperature ranges from less than -200° F to more than 200° F.e