Blue Skies and Colourful Sunsets

Click here to listen to this feature  

Have you ever wondered what causes those beautiful blue skies, and romantic sunsets? It's all caused by the mixture of gases in our atmosphere, which scatter the components of white sunlight.

Light from the sun is made up of a spectrum of colours - going from red to blue, like a rainbow. Air molecules scatter some of the components of sunlight more than others. They scatter the blue component of light about ten times more than the red. In fact, the blue part of the light is constantly re-scattered, while the other colours continue more or less on their original path.

When you lie on the beach gazing at the sky, you see all that extra blue light that has been scattered in your direction. If, however, you were vacationing on the moon, your holiday pictures would have no blue background, because there are no air molecules to scatter the light.

But back to Earth, what about those beautiful reds and pinks we see if we stay on the beach until sunset? As the sun goes down, the light travels through more atmosphere to reach us, losing more of its blue component. We then see more of the red and orange colours. Clouds further enhance sunsets, because their water droplets reflect and amplify the red and orange shades in the darkening sky.

So next time you watch a sunset, thank those little molecules that scatter the light, and bring such beauty to the heavens.