Because the air scatters blue light around much better than it does red.

In 1914 he showed that pure gases could scatter light.

Dust high in the atmosphere scatters light to the night side of the planet.

The Spirit shook his head, scattering light from his hair as he did so.

This technology scatters infrared light, which is invisible to the human eye, in unique ways.

Small air molecules scatter blue light more efficiently out of the direct sun rays, and that is what we see.

There were tiny lights scattered around the tank cover.

Luke looked outside at lights scattered like distant stars through the pre-dawn dark.

Water, containing little particulate matter, scatters light in the blue region of the spectrum.

The blue colour is produced by air bubbles in the feathers which scatter light.