Why Autumn Skies Are So Blue

blue sky and sun through foliage
Paul Zizka/All Canada Photos/Getty Images

Have you ever noticed that fall skies appear to be a deeper, more saturated blue than normal?  What sorts of things can make the sky appear bluer, specifically during the fall season? Here are a few contributing factors:

Fall's Lower Humidity

Fall is notorious for its pleasant weather--namely, its cooler temperatures and lower relative humidity. As air temperatures cool, the amount of moisture that the air can hold lessens. Less moisture means fewer clouds and haze occupying skies in September, October, and November. With little to no clouds or haze to veil the sky, its blue hue appears purer, and the sky itself, more open and vast.

Fall's Lower Sun Position

As we progress through autumn, the sun "sits" lower and lower in the sky. With the sun no longer directly overhead, you could say that more of the sky is significantly angled away from the sun. The Rayleigh scattering directs more blue light towards your eyes, while the indirect sunlight decreases the incoming levels of red and green--the result of which is a more intense blue sky.

Fall's Foliage

Believe it or not, the very presence of fall's red, orange, and gold leaves actually help give the sky's blueness a color boost. According to color theory, primary colors appear more brilliant when they're in contrast with their complementary colors. Looking at a color wheel, you can see that violet and blue (which are the two wavelengths of sunlight that are scattered for us to see and thus give the sky its characteristic blue hue) correspond to the complementary colors of yellow, yellow-orange, and orange. Seeing any one of these leaf colors against the backdrop of a clear blue sky makes the blue of the sky "pop" that much more.

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Means, Tiffany. "Why Autumn Skies Are So Blue." ThoughtCo, Apr. 5, 2023, thoughtco.com/why-autumn-skies-so-strikingly-blue-3443599. Means, Tiffany. (2023, April 5). Why Autumn Skies Are So Blue. Retrieved from https://www.thoughtco.com/why-autumn-skies-so-strikingly-blue-3443599 Means, Tiffany. "Why Autumn Skies Are So Blue." ThoughtCo. https://www.thoughtco.com/why-autumn-skies-so-strikingly-blue-3443599 (accessed June 3, 2023).