Ashwem Beach, Goa
Why does the sea come up the beach?
01
Look up. The Moon!
The Moon pulls the sea. Like a magnet.
The sea bumps up toward it.
Drag the Moon. The sea follows!
02
Why two bumps?
Three friends race to the Moon. The Moon pulls the closest friend hardest. So they spread out!
The Earth is full of friends. It gets stretched. A bump in front, a bump behind.
03
The Earth spins round.
Your beach goes round and round. Under a bump: water up! Between the bumps: water down.
Two bumps. So, twice a day.
Water up!
04
The Sun helps a little.
The Sun pulls the sea too, but it is far, far away.
Sun and Moon pulling together: a BIG bump. Pulling sideways: a small bump.
For grown-ups
Why the Moon beats the Sun.
The Sun pulls the Earth 180 times harder than the Moon does. So why does the Moon run the tides?
Pull on the Earth
Pull is about mass. That is why we go round the Sun.
Stretch across the Earth
Tides are about the difference between the pull on the near side and the far side. That difference fades with distance cubed, and the Moon is 390 times closer.
The space pictures look down on the North Pole. The Moon is drawn ten to twenty times too close, and the bumps thousands of times too tall: on the open sea the real bump is under a metre, and coasts funnel it into the tides you see. Your beach is Ashwem Beach, Goa. Scene 04 starts from today's real Moon.