Trail in Namibia Trail in Namibia

Rayleigh Scattering

However clear the sky, however free from even the wispiest of clouds, the sky is never uniformly blue.

It is always closer to white near the horizon, due to an effect caused by ‘Rayleigh scattering’.

This is worth knowing if you’re doing any natural weather forecasting, as otherwise it can catch you out, making it appear that there are clouds in the distance when there are none.

Rayleigh scattering is also the reason that more distant hills appear a lighter colour than in those closer to us.