Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air.

Blue light is scattered more than the other colours because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

As white light passes through our atmosphere, tiny air molecules cause it to ‘scatter’.

The scattering caused by these tiny air molecules (known as Rayleigh scattering) increases as the wavelength of light decreases.

Violet and blue light have the shortest wavelengths and red light has the longest.

Therefore, blue light is scattered more than red light and the sky appears blue during the day.

So why do sunsets appear red? When the sun is lower in the sky, sunlight travels a longer distance through the atmosphere to reach an observer.

This means it encounters more particles that scatter out most of the blue light, as well as some green and yellow light.

This leaves mostly red light when the sunlight reaches the observer.