🌕 Tides and the Moon

Why the sea comes up the beach and goes back out twice a day: the Moon is pulling it.

Two tides a day
At most beaches, the sea creeps up the sand and then slides back out again, twice a day. That rise and fall is the tide. What makes it? The Moon!
Drag the Moon
The Moon’s gravity pulls on the sea. It makes the sea bulge out in two places: under the Moon, and on the other side of the Earth. Drag the Moon round and watch the blue bulges follow.
Why two bulges?
The Moon pulls hardest on the side of the Earth nearest to it, and least on the far side. So the near sea is pulled towards the Moon, and the far sea gets left behind, like a ball flung on a string. That makes two bulges.
Spin through the bulges
The Earth spins round once a day, under the bulges. Slide the clock and watch the beach in Ghana. How many high tides does it get?
Take away the Moon
The Sun pulls on the sea too. It is much bigger than the Moon, but much further away, so its pull on the tides is smaller. Tap the button to take the Moon away.
Quiz time
The shape of the coast changes the tides a lot. In one long, narrow bay in Canada, the sea goes up and down more than anywhere else on Earth.

⭐ Remember

The Moon’s gravity pulls the sea into two bulges, one on each side of the Earth.
As the Earth spins, most beaches pass through both bulges: two high tides a day.
The Sun makes tides too, but they are only about half as big.

The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).