Video narration
Sunlight looks white, but it’s actually a mix of many colors. When that sunlight enters Earth’s atmosphere, it runs into tiny air molecules. Those molecules scatter light in different directions, and they scatter short-wavelength colors—like blue—much more than long-wavelength colors—like red. So as sunlight travels through the air, blue light gets bounced around and spread across the whole sky. That means when you look up, blue light is coming to your eyes from nearly every direction, not just straight from the Sun. Red light, which scatters less, mostly keeps going forward. So the sky isn’t blue because the air is blue—it’s blue because the atmosphere spreads blue light around more strongly than other colors.