Twilight skies: What causes the explosion of colours?

As soon as the sun goes down, sunlight is by no means over. Twilight offers an explosion of colours in the sky for us to marvel at.

Twilight is the transitional period between day and night. In the evening it is called dusk, in the morning, dawn. Air molecules, aerosols and cloud droplets trigger the blaze of colour in the sky that often accompanies twilight.

Tiny particles in the atmosphere are responsible for the colours lighting up the sky. When the sun is only slightly above the horizon, light takes a longer path through the atmosphere, than when the sun is higher up.

The influence of air molecules and aerosols, such as dust, increases the closer the sun is to the horizon. As shorter wavelengths (blue tones) are scattered more strongly, the sky turns a yellowish-red.

After sunset, the colours become even more intense because the low angle of the sun also illuminates the clouds.

Long after sunset, when the first stars twinkle, the sky turns deep blue. Although all the sun's rays have travelled a long way through the atmosphere, the blue colour components dominate once again.

This blue is a result of the stratospheric ozone layer at an altitude of 20 to 30 kilometres. Here, ozone molecules absorb the orange part of the light.

The selective absorption shifts the colours to the shorter wavelengths, i.e. to blue. When the sun is low, the ozone layer acts like a blue colour filter and we can see it with the naked eye.

Keep an eye out for our tips coming soon on how to photograph at twilight!