How many time have you used that phrase, "dark side of the moon?" Maybe not many. Other than as the title of a very popular Pink Floyd CD, I don't believe the saying is used much anymore.

That's because "dark side" isn't the correct way to refer to the part of the Moon that we don't see as it orbits Earth. In the past people thought one side of the Moon was always dark, hence the phrase "dark side of the moon." It actually turns out that the side of the Moon we see in our skies actually gets dark each month as often as the other side does.

Call It What It Is: The Far Side

The better term to use is the "far side". Here's why: the orbit of the Moon is such that one rotation takes just about the same length of time as Moon's orbit around Earth. That is, the Moon spins on its axis once during its orbit around our planet. That leaves one side is facing us during its orbit. The technical name for this spin-orbit lock is "tidal locking".

Of course, there is literally a dark side of the Moon, but it doesn't stay dark all the time, and it's not the same side all the time. During a new moon, the moon lies between Earth and the Sun. So, the side we normally see all lit up is tot.