Behind the Forecast: Why the sky isn’t really as blue as you think

Listen to Science Behind the Forecast with Meteorologist Tawana Andrew every Friday on 89.3 WFPL at 7:45 a.m.
Published: Oct. 8, 2021 at 11:48 AM EDT
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LOUISVILLE, Ky. (WAVE) - The sky is blue. Right? Well, it is, but it also isn’t.

White light from the sun is a combination of every color in the rainbow. Each color we see corresponds to a particular wavelength. The visible light spectrum ranges from violet, with a wavelength around 380 nanometers, to red, which has a wavelength around 720 nanometers.

Particulates and gases in our atmosphere scatter sunlight. Because of its shorter wavelength, violet light is scattered first high in the atmosphere. Indigo light waves are scattered next, followed by blue. Molecules in our atmosphere scatter blue light four times as much as red light. Most of the sunlight that actually enters our atmosphere is blue, not violet. However, technically, violet light is scattered the most, so the sky is actually a blueish violet.

Biology is part of the reason we see the sky as blue. Those color-sensitive cones in our eyes react most strongly to blue, green, and red wavelengths; this is why we see colors the way we do. Blue and violet light react with not just the blue cones in our eyes, but they also interact with the red and green cones slightly. When our eyes see the red tinge to violet and the green tinge to blue, these are negated; thus allowing us to see a blue sky.

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