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What are tides?

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Quick answer

Tides are the regular rise and fall of the ocean's surface, caused mainly by the Moon's gravity pulling on Earth's water. As Earth rotates, most coasts get two high tides and two low tides each day. The Moon's gravity tugs the oceans, bulging the water toward it.

Key things to understand

  1. The Moon's gravity tugs the oceans, bulging the water toward it.
  2. Earth's rotation moves coastlines through these bulges, giving two tides a day.
  3. The Sun's gravity adds to the effect, creating stronger 'spring' tides.
  4. When Sun and Moon pull at right angles, weaker 'neap' tides occur.

People also ask

What causes tides?
Mostly the Moon's gravity pulling on Earth's oceans, with a smaller contribution from the Sun.
Why are there two high tides a day?
The ocean bulges both toward and away from the Moon, so a rotating coast passes through two bulges daily.
What are spring and neap tides?
Spring tides are extra-large when Sun and Moon align; neap tides are smaller when they pull at right angles.

Part of the guide: Water & Weather Phenomena →