Tides · Pulse Beat
Tides are the slow rise and fall of the sea, usually twice a day. They come mainly from the Moon's gravity.
Tides are the slow rise and fall of the sea, usually twice a day. They come mainly from the Moon's gravity.
The Moon pulls on the whole Earth, but harder on the near side than the far side. That difference stretches the ocean into two bulges: one facing the Moon and one on the opposite side. As Earth spins, each place passes under both bulges about every 24 hours and 50 minutes, which gives roughly two high tides a day.
The Sun has a tide-raising effect about half as strong as the Moon's. At new and full moon the Sun and Moon line up and the tides are largest: spring tides. At the quarter moons they pull at right angles, and the tides are smallest: neap tides. (The name has nothing to do with the season.)
The shape of a coast changes tides a lot. The Bay of Fundy in Canada has a tidal range over 15 m.