Why the Sky Is Blue
The sky looks blue because gas molecules in the atmosphere scatter short-wavelength blue light far more strongly than red light. Sunsets look red and orange because blue light is scattered out of the direct beam over the longer path.
Not factually verified. This thread was posted by a member and nobody has checked it. Read it as one person’s account and check the sources yourself.
Scattering of sunlight
Sunlight looks white but contains a mix of all colours. When it enters the atmosphere, it collides with gas molecules, mostly nitrogen and oxygen, which are much smaller than the wavelength of visible light. This kind of scattering is called Rayleigh scattering. It is much stronger for short wavelengths: blue light is scattered roughly ten times more strongly than red light. As a result, blue light is bounced around the whole sky and reaches the eye from every direction.
Why the sky is not violet
Violet light has an even shorter wavelength and is scattered even more. However, the Sun emits less violet than blue, some violet is absorbed high in the atmosphere, and human eyes are less sensitive to violet. The mix of light that reaches the eye is therefore interpreted as blue.
Sunsets
At sunset, light travels through much more atmosphere to reach the observer. Most of the blue light has been scattered out of the direct beam along the way, which leaves reds and oranges. Lord Rayleigh worked out the mathematics behind this scattering in the 1870s.
Sources
- NASA, Space Place: Blue Sky explanation Added by the author.