Before we can understand why the sky looks bluer in the fall, it's important to first know why the sky appears blue in the first place.
WHY IS THE SKY BLUE?
The sun emits white light, and due to Rayleigh scattering (the scattering of light by air molecules), blue light scatters more easily because it has a shorter wavelength and travels through less atmosphere. This scattering is why the sky appears blue to our eyes during the day.
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WHY DOES THE SKY APPEAR MORE BLUE?
This deep blue hue is common in the fall and can last into early spring. As the temperatures drop and daylight hours decrease, humidity levels also fall.
Lower humidity and drier air mean less scattering of blue light, allowing more blue to reach our eyes and making the sky appear more intensely blue.
The changing color of the leaves also plays a role. Fall colors like red, orange, and yellow are complementary to blue, meaning they contrast with it and make the blue appear even more vivid.
