What happens when light enters a transparent medium like our atmosphere: It slows down

Snell 's window shows you a fish-eye view that shows you not just the sky, but the side of the pool.

This cool effect is caused by the optical properties of water.

The higher the index of refraction, the slower light travels in that medium.

Changing speed also causes the direction of the light to change.

If you are underwater and you want to see something above the water, light from that object has to travel in such a way that it enters your eye.

But as the light source is rotated toward the horizon, resulting in larger angles of incidence, the light bends as it enters the water.

If you point to where you see the bird through Snell 's window, you'll be pointing at empty sky.

If you look at a fiber-optic cable, the ends look bright because light can enter the sides but only exit through the ends. This is quite useful for sending data from one place to another. It turns out that by using light, you can transmit data at a much higher rate than by electrical signals, so it's great for streaming hi-def videos of spearfishing. But don't worry, if you don't have fiber-optic internet at home, you can just go outside and jump in the swimming pool. And be sure to look for Snell 's window!.