If you REALLY watch the moon — the way the Babylonians did 3,700 years ago — you'll notice that its path keeps changing. We're not talking about super-obvious lunar behavior like its rapid sky movement, or the nightly shift in where it rises and sets. Some years the moon's nightly motion can mimic the sun's daytime path across the sky. Other years the moon never quite ascends as high as the sun. But the most dramatic part of the cycle is the brief three-year period when the moon gets much higher than the sun.