Snell's window

Hey kiddo, today I will tell you about Snell's window!

You know when you look into a swimming pool, things underwater look different than when they are above the water? That's because of Snell's window.

Snell's window happens because of how light travels through the water. Light can bend, or change direction, when it travels from one place, like air, to another place, like water. This is called refraction.

When light travels from air into the water, it refracts and bends. The light that comes in at a very steep angle, like from the sides of the pool, gets bent a lot and goes away from you. So, you can't see things underwater that are at a steep angle to the surface of the water.

But the light that comes straight from the bottom of the pool goes straight to your eyes without bending too much, and that's what you call Snell's window!

So if you look at something underwater, like a fish, that is in line with the surface of the water, it looks like it's not too deep, even if it's very far down. This is because Snell's window makes it look like it's closer to the surface than it actually is.

Isn't that cool? That's Snell's window!