Why is the sky blue? 🪟🌞
Our blue sky demonstration is a demonstration of Rayleigh Scattering. A tube is filled with water and then we added polystyrene latex spheres into the water that were 200 nanometers (nm) in diameter. The spheres are smaller than the wavelength of visible light, which ranges from around 400nm to 750nm, which allows the visible light to scatter strongly off of the spheres without loss in energy, similar to how it would scatter off of the air molecules. One way to think about the scattering of light is to imagine how electrons in the nitrogen and oxygen molecules oscillate in the alternating electric field of the incoming light. The oscillating electrons produce light of the same frequency of the incoming light, but this light goes off in all directions. Rayleigh scattering is wavelength dependent and shorter wavelengths of light, such as blue light, scatter stronger than longer wavelengths of light, such as red light. During the middle of the day, the light from the sun has the shortest path to our eyes because it passes through a shorter distance in the atmosphere. The blue light from sunlight scatters more than the red light does, and so the sky appears blue. During sunrise and sunset, the light has to pass through more atmosphere to reach our eyes so the blue light has already been largely removed, and what is left over are the yellow, oranges and reds which we observe during those beautiful hours.
See our related video on how you can make your own sunset.
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