How do the Moon and Sun cause tides?

The Moon pulls the near side of the Earth harder than the far side, and the water is stretched into two bulges along the Earth-Moon line. The Sun makes smaller bulges in the same way. As the Earth turns, a coast passes through both bulges each day.

What are spring tides?

Spring tides happen at new and full Moon, when the Sun and Moon pull in one line. The two bulges add up, so high tides are highest and low tides are lowest.

Neap tides happen at the first and last quarter Moon, when the Sun and Moon are at right angles. The Sun pulls across the Moon, the bulges partly cancel and the tidal range is smallest.

Why are there two high tides a day?

There are two bulges, one under the Moon and one on the far side. The Earth turns under both in about 24 hours 50 minutes, so a coast has two high tides about 12 hours 25 minutes apart.

How long is a lunar month?

The Moon takes about 27.3 days to go round the Earth against the stars, and about 29.5 days from one new Moon to the next, because the Earth moves round the Sun too.

🌍 Geography · How water, weather and the land move

Tides & the Moon

Drag the Moon around the Earth and watch the two tidal bulges follow it.

Tides & the Moon

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