The blue color of the sky is caused by the scattering of sunlight off the molecules of the atmosphere. Scattering is when light hits a molecule and bounces off in a different direction. Shorter wavelengths, toward the blue end of the spectrum, scatter more strongly than longer wavelengths (red end of the spectrum). Hence the scattered light contains much more blue light than red. The scattering is strongest 90 degrees away from the sun.
Philip P.
tutor
I learned about Rayleigh Scattering in my Intermediate Electromagnetic Theory course in college. Molecules consist of bound positive and negative charges. When excited by incoming light, the molecules vibrate and act like little antennas, re-radiating the incoming light at all angles. The antenna effect is strongest in blue light. Remember, color is just light of different frequencies. If something looks blue, it's because blue light is reflected off the object more strongly than other colors, making the object appear blue. So if the sky looks blue, it's because blue light is scattered off of it more strongly than other colors.
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11/19/18
Philip P.
tutor
Another important fact to note is that in places like the moon, there is no atmosphere so the sky is not blue. In fact, the sky on the moon is dark at all times, even during the day; and you can see stars during the day. The ground is bright but the sky is dark because there is no air to scatter light.
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11/19/18
Tanner G.
Why do shorter wavelengths scatter more strongly?
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05/07/22
Philip P.
tutor
Every oscillator has a preferred frequency, called its resonance, that it wants to vibrate at. If you vibrate the oscillator at or near its resonant frequency, it will vibrate readily. If you try to vibrate the oscillator at frequencies not close to its resonant frequency, it will not vibrate as much. For air molecules, the higher frequencies of light - that is, blue light - are closer to the resonant frequency of the molecules.
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05/07/22
Morgan B.
thats just a thing you found on the internet11/19/18