That also explains why the moon sometimes rises in the evening and us up during the night, while at other times it's up only or mostly during the day.
Long ago, the Earth's gravitational effects slowed the moon's rotation about its axis. Once the moon's rotation slowed enough to match its orbital period (the time it takes the moon to go around Earth) the effect stabilized.
So the moon goes around the Earth once and spins on its axis once, all in the same amount of time, and it shows us just one face the whole time.
When a full moon rises while it's at apogee, the disk we see can be 14 percent bigger and 30 percent brighter than other full moons.
The moon is not bigger when it rises compared to later at night, however; that's an illusion (one that causes a lot of argument over what causes it). You can test this yourself by holding something about the size of a pencil eraser at arms-length when the moon first rises and looks so huge, then repeat the test later in the evening when the moon is higher and looks smaller. Next to your eraser, it'll look comparatively the same in both tests.
By dating the moon's many craters, scientists figured out that the moon (and Earth) underwent a Late Heavy Bombardment around 4 billion years ago. The latest thinking on this pummeling is that life may have survived it, if biology had gotten a foothold that early.
Small moonquakes, originating several miles (kilometers) below the surface, are thought to be caused by the gravitational pull of Earth. Sometimes tiny fractures appear at the surface, and gas escapes.
Scientists say they think the moon probably has a core that is hot and perhaps partially molten, as is Earth's core. But data from NASA's Lunar Prospector spacecraft showed in 1999 that the moon's core is small — probably between 2 percent and 4 percent of its mass. This is tiny compared with Earth, in which the iron core makes up about 30 percent of the planet's mass.
One engineer thinks these moonquakes should be taken into account when future lunar bases are designed.
The moon's gravity pulls on Earth's oceans. 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.
At full moon and new moon, the sun, Earth and moon are lined up, producing higher than normal tides (called spring tides, for the way they spring up). When the moon is at first or last quarter, smaller neap tides form. The moon's 29.5-day orbit around Earth is not quite circular. When the moon is closest to Earth (called its perigee), spring tides are even higher, and they're called perigean spring tides.
All this tugging has another interesting effect: Some of Earth's rotational energy is stolen by the moon, causing our planet to slow down by about 1.5 milliseconds every century.
Researchers say that when it formed about 4.6 billion years ago, the moon was about 14,000 miles (22,530 kilometers) from Earth. It's now more than 280,000 miles, or 450,000 kilometers away.
Meanwhile, Earth's rotation rate is slowing down — our days are getting longer and longer. Eventually, our planet's tidal bulges will be assembled along an imaginary line running through the centers of both Earth and the moon, and our planetary rotational change will pretty much cease. Earth's day will be a month long. When this happens, billions of years from now, the terrestrial month will be longer — about 40 of our current days — because during all this time the moon will continue moving away.