Why is the sky blue during the day but red at sunset?

Sunlight looks white, but it’s actually made of every color mixed together. As it travels through the atmosphere, it bumps into tiny gas molecules that scatter blue light far more than other colors — that’s why we see blue when we look up. At sunset, the sun’s light has to pass through much more atmosphere to reach our eyes, which scatters away almost all the blue, leaving the longer red and orange wavelengths to reach us instead.