The Moon is Receding, and the Tides are to Blame
The Moon gets further from the Earth by about 4 cm per year.
The graphic helps understand why:
1. The Moon raises tidal bulges in the Earth’s oceans.
2. As the Earth rotates, friction causes the tidal bulge to be pulled in the rotation direction, so that it is not directly under the Moon.
3. The water in the bulge exerts a small gravity force on the Moon. Because of the bulge’s offset, part of this force is to the left, and this causes the Moon to speed up slightly.
4. As it speeds up, the size of its orbit increases.
Distance measurements using lasers are so precise that the increase in orbit size has been verified. In a few hundred million years, the Moon will be far enough away that it can no longer cover the Sun, and there will be no more total solar eclipses.
The same phenomenon causes the Earth’s rotation rate to slow down. The total Earth-Moon angular momentum must remain constant, and as the Earth imparts angular momentum to the Moon, the Earth’s angular momentum (and rotation rate) must decrease.#physics #Moon #gravity