Red sunsets happen because sunlight travels through more air and loses its blue wavelengths.

The longer version

At sunrise and sunset, sunlight slants in through a much longer path of atmosphere than at midday. Along that path, air molecules and small particles scatter the short wavelengths of light, the blues and violets, out of the beam in every direction.

What survives to reach the eye is the remaining longer wavelengths, which is why a low sun looks orange or red. Dust, smoke, and water droplets in the air can deepen the colour further, which is why hazy air so often produces the reddest skies. The same scattering during the day is what makes the open sky look blue.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.