Asked by irinamartis to Anna, Daniel, Denise, Jesse, Rehemat on 25 Jun 2014.
Keywords: blue, sky
A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
Hope it helps! 🙂
Indeed it’s a question of light “reflection”. The molecules constituting our atmosphere “reflect” light in a specific way, that is called “Rayleigh scattering”. This kind of scattering is special because reflect light of different colours in a different way. In particular it reflects much more the blue colour. Why? I do not know if you are familiar with the concept of “wavelength”. Light, as you might know, can be described as a wave. To each colour we associate a wave that has a different length between two consecutive crests (or two troughs), and we call this length “wavelength”. The Rayleigh scattering reflects much more waves with small wavelength, and guess which colour has a very small wavelength? Blue, of course 😉 with a wavelength of about 475 nm (0.000000001 meters). For a comparison, red has a wavelength of about 650 nm.
Great question! And Anna and Denise have given excellent answers 🙂 I guess that I could just add an example of this that you might have seen before that diffracts light like the molecules in air do, as Anna and Denise said. Try using a kaleidoscope or a piece of quartz, these diffract light with the same principles that Anna and Denise described below! Hope this helps!
The color of the sky depends on how light is refracted in the atmosphere. Notice how colors change from early morning to noon and back to sunset. There is usually reddish colors in the morning and sunset, and blue during most of the day. During early morning and afternoon the light has to travel farther in the sky and the cooler colors like blue are refracted and what you see is red and orange, warmer colors. During noon, the light travels a shorter distance and the cooler color ( blue) has not refracted completely and dominates the sky.
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