Why the sky is blue and sunsets red
To understand why we see the sky as blue and sunsets as red or orangewe need to understand a little bit about how light is made up of a spectrum of colours.
The sky appears blue because of a phenomenon called Rayleigh scattering. Sunlightalthough it looks whiteis actually made up of many colourseach with a different wavelength. At one end of the spectrum is red light which has the longest wavelength and at the other are blue and violet light which have a much shorter wavelength. When sunlight enters Earth’s atmosphereit collides with tiny gas molecules - mainly nitrogen and oxygen. These molecules are much smaller than the wavelength of visible lightso they scatter shorter wavelengths much more than longer wavelengths.
Even though violet light is scattered even more than blueour eyes are more sensitive to blueand there’s less violet in sunlight to begin with. That’s why we see a blue sky instead of a purple one.
Why does the blue fade at the horizon?
The sky looks most vibrant overhead and paler near the horizon. This happens because light from the horizon travels through more atmospheregetting scattered and re-scattered along the way. The increased scattering mixes in more white lightmaking the blue less intense.
Why are sunsets red or orange?
Againthis is to do with Rayleigh scattering and the fact that light is made up of many different colours of differing wavelengths.
Blue and violet light gets scattered more than other colours because it travels as shortersmaller waves. At sunrise and sunsetthe Sun is low in the skyso its light passes through a thicker layer of atmosphere. The shorter wavelength blue light is scattered furtheras the sunlight passes over a greater distanceand we see the longer wavelengths—reds and oranges—that create those beautiful sunset and sunrise colours.
In summarythe colours we see in the sky are all about how sunlight interacts with the atmosphere. Blue skies and red sunsets are both results of the same scattering processjust seen from different angles and at different times of day.
