What Are Moon Librations and What Causes Them?

Believe it or not, the moon nods both yes and no.

The nods or movements are called librations. The slow nod “no” from side to side, which lets us see first one “cheek” of the moon and then the other, is called longitudinal libration.

The nod “yes,” which shows us the “forehead” and then the “chin” of the moon, is called latitudinal libration. Don’t stand outside in the cold waiting for the man in the moon to nod to you, though.

It takes two weeks for him to move his head downward and another two weeks to bring it back up again to complete the nod. Longitudinal librations are caused by changes in the speed at which the moon orbits the earth.

Latitudinal librations are caused by the tilting of the moon on its axis as it makes this orbit.