Tides: The Moon’s Hidden Grip on Earth

Tides happen because gravity pulls differently on different parts of Earth. The Moon pulls slightly more strongly on the side of Earth closest to it, creating a bulge. There’s also a second bulge on the opposite side due to the Earth–Moon system’s motion.

As Earth rotates, coastlines move through these bulges, producing high and low tides. The Sun also contributes, and when the Sun and Moon line up (new moon and full moon), tides can be stronger—these are spring tides (nothing to do with the season).

Over very long time spans, tidal forces can slow rotation and shift orbits. The Moon is slowly drifting away from Earth, just a tiny bit each year.