The sky appears blue because of a phenomenon called Rayleigh scattering. Sunlight may look white, but it’s actually made of different colors—just like a rainbow. Each color of light travels in waves, and blue light has shorter, smaller waves compared to other colors. When sunlight hits the Earth’s atmosphere, these shorter blue waves are scattered in all directions by the air.

Because blue light is scattered more than other colors, it’s the one we see most when we look up. Even though all colors are scattered a little, blue dominates because its wavelength interacts more easily with the tiny particles and gas molecules in the air. That’s why the sky looks blue during the day, especially when the sun is high.

At sunrise and sunset, the sky can change color because the sun is lower on the horizon, and the light travels through more atmosphere. This causes more scattering of the blue light, leaving the reds and oranges behind. But during most of the day, it’s blue that fills our sky, thanks to how sunlight and air work together.