Red Sky at night scientist's delight

The sun’s changing colours at sunset (and sunrise) are the result of us seeing the rising and setting sun through our atmosphere. When the sun is high in the sky, we are looking directly at it, so only a thin layer of air lies in the way. At sunset, though, we are looking towards the horizon through a much thicker layer of atmosphere.

As the light from the sun enters the earth’s atmosphere it is affected by air molecules. Individual photons of light collide with these molecules and are bounced of, scattering in different directions depending on their wavelength and colour. Blue light has the shortest wavelength so and is scattered the most, so as previously posted, the sky looks blue.

At sunset, the scattering effect increases as the light has to travel a greater distance through the atmosphere.First green then yellow are affected, until finally the only light we see directly from the sun is orangey-red giving it its red glow.