The Sky

Without sunlight, we would not only be in darkness, but the world would also be completely devoid of colour. As a general rule, sunlight appears to us as a pale whitish-yellow, but it is actually made up of the whole spectrum of colours visible to the human eye – literally, all the colours of the rainbow.

The coloured components of the Sun’s light becomes visible when it is broken up as a result of refraction and scattering in the atmosphere. During the day, the sky is predominantly blue because many different solid and gaseous particles in the atmosphere scatter the sunlight in a particular way.

The British physicist Lord Rayleigh (1842–1919) was the first to come up with a conclusive explanation of the sky’s blue colour – which is why the phenomenon is known as Rayleigh scattering.

Why are dawn and sunset skies often red?

The explanation for the reddish tints seen in the sky at either end of the day also lies in Rayleigh scattering. As it passes through layers in the atmosphere, light with shorter wavelengths is scattered more than light with longer wavelengths.

For this reason, blue light, with its short wavelength, is scattered more than red light. When the Sun is high in the sky, and the journey that sunlight takes through the atmosphere is relatively short, blue is predominantly scattered and the result is a blue sky.

When the sun is low, the light travels much further through the atmosphere and scattering reduces the blue content to such a degree that red predominates. Blue is literally scattered away. This is why the sky is red at sunrise and sunset. Sunlit clouds and droplets of water in the air further intensify the red tint.