Why Is The Sunset Red?

The sky turns red during sunset because light travels through more air when the sun is low.

Imagine you're playing with a flashlight in a room full of tiny dust particles. When you shine it straight ahead, the light goes through just a little dust. But if you tilt the flashlight so the light bounces around the room, it passes through much more dust, and that makes the light look yellow or even red, like when you squint at a bright lamp in a foggy room.

During the day, sunlight comes straight down, passing through less air. That's why the sky looks blue, blue light is scattered more easily by the tiny particles in the air.

But during sunset, the sun is low on the horizon, so its light has to travel through much more of Earth’s atmosphere. This means the blue and green light get scattered away, leaving mostly red and orange light to reach your eyes, that's why the sky looks red or pink.

It’s like when you look at a glass of water with a straw in it, the part of the straw under the water looks bent because light changes direction as it moves from air into water. Similarly, sunlight bends and changes color as it passes through more air during sunset.