Why are sunsets red?

Sunsets look red because sunlight reaches you through a much longer path of air when the Sun is low. Air scatters blue and violet light more easily, while red and orange travel farther, so those warmer colors are what your eyes receive near the horizon.

The Sun itself has not changed; the atmosphere is sorting its colors. Tiny molecules, dust, and droplets can make the effect stronger, which is why a hazy evening may turn the sky pink, copper, or deep red before the light fades.