ELI5: What causes ocean tides?

Imagine the Earth is like a big bouncy ball covered in water. Now, think of the Moon as another smaller bouncy ball that's pulling on the Earth's water!

The Moon has a special power called gravity. Gravity is like an invisible rope that pulls things together. The bigger something is, and the closer it is, the stronger its gravity.

Here's what happens:

• The Moon's gravity pulls on the side of the Earth closest to it. This pull makes the water bulge out – that's a high tide!

• But here's a trick! The Moon also pulls on the whole Earth, so the side of the Earth furthest from the Moon also bulges out. This is because the Earth is being pulled away from the water on that side. So, there's another high tide on the opposite side of the Earth!

• In between the two bulges, the water gets thinner, creating low tides.

The Sun also has gravity, but it's much further away than the Moon. So, the Sun's effect on the tides is smaller. When the Sun and Moon line up (during new and full moons), their gravity works together, creating even bigger high tides (called spring tides). When the Sun and Moon are at right angles to each other (during quarter moons), their gravity partially cancels out, creating smaller high tides (called neap tides).

So, the Moon, and a little bit the Sun, are the puppet masters that control the ocean tides! It's all about gravity!