Earth & Space

Why there are two high tides a day: the Moon pulls the near sea harder and the far sea softer

Top-down Earth with its ocean stretched into two bulges, one toward the Moon and one away
30seconds
The 30-second version

The sea rises twice a day, not once, and the second high tide happens on the side of the Earth facing away from the Moon. Why?

The Moon pulls the near ocean a little harder than the Earth's centre and the far ocean a little softer. Once the shared pull is cancelled by free fall, only those small differences remain, and they stretch the water into two bulges.

Drag the Moon around the Earth, add the Sun, and read a live tide gauge to see why highs arrive about 12 h 25 min apart and what makes spring and neap tides.

Deep dive · 4 min

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