Sun · Earth · Moon · Ocean
Use the arrow buttons to run time forward or back, or tap a preset to jump to a spring, normal or neap tide. Watch the ocean bulges from above and the water rising and falling at the harbor.
Show me a tide
Rising tide
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The Moon pulls the near-side ocean a little harder than it pulls Earth’s center, and pulls Earth’s center a little harder than the far-side ocean. That difference stretches the ocean both ways at once. As Earth turns through both bulges, most coasts get two high tides and two low tides a day.
The word means “springing up.” Spring tides happen twice a month, at new and full moon, when the Sun’s and Moon’s bulges line up and add together. Neap tides happen at the quarter moons, when the two bulges are at right angles and partly cancel.
The Sun’s pull on Earth is about 180× the Moon’s. Tides, though, come from the difference in pull from one side of Earth to the other, and that drops off with the cube of distance. So the Sun’s tide ends up only about 46% as big as the Moon’s.
While Earth spins, the Moon keeps moving along its orbit, so each spot on Earth needs about 50 extra minutes to face it again. High tides come about 12 h 25 min apart, so each day’s tides are roughly an hour later than the day before.