Fact or Faux: Are skies really more blue during fall than in summer?

Weather Blog

ROCHESTER, N.Y. (WROC) — Have you looked up at the sky lately? A question that often comes up this time of year is whether or not the sky looks more blue during the fall than in the summer.

FACT: The answer to that is yes, and it’s not just a coincidence!

How it works:

The way our eyes interpret colors are from light on the visible spectrum. When white light travels through a prism, it scatters the light into all the colors from the rainbow.

The color we see as a result has to do with how sunlight is scattered off of the molecules in the earth’s atmosphere. As sunlight reaches the atmosphere, a process called Rayleigh scattering makes it so that the blue light is the dominant color reaching our eyes.

Image courtesy: wildcardweather.com

Rayleigh scattering is the scattering of light molecules that are approximately 1/16 the wavelength of the light, and can be represented by this equation:

Image courtesy: hyperphysics.phy-astr.gsu.edu

The smaller the number of the wavelength, the more Rayleigh scattering you get as a result.

Blue and purple light have the shortest wavelengths on the spectrum while red has the longest. With the blue wavelength being shorter, it’s easier to scatter and therefore the sky appears blue!

But why does the sky look more blue this time of year?

The reason that the blue color appears more vibrant to us during the fall and even winter seasons has to do with a couple of things.

A key player is the lower levels of moisture you find a lot more often during the cold season than in the warm season. During summer there’s a lot more moisture in the air which not only makes it more humid, but the more water vapor present means there are are molecules around to scatter the blue light, so the sky appears more dull and less vibrant.

The more Rayleigh scattering occurring, the more blue the sky looks. This is much easier to accomplish during the Fall and winter season when it’s cold and drier. With less particles and moisture to scatter through the atmosphere, a bluer sky appears as a result!

The angle that the sun rises to during the year plays a role too. With the sun at an angle there’s more Raleigh scattering occurring, and paired with the lack of moisture present you can get really deep blue skies out of it.

A similar concept known as Mie scattering explains why we see the red color in sunsets as light passes through a thicker atmosphere with more particles in it.

It’s these bluer looking skies that make the fall colors on the leaves really pop this time of year. Next time you’re outside, go ahead and see if you notice the difference!

~Meteorologist Christine Gregory

Copyright 2021 Nexstar Media Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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