Science, Tech, Math › Science Why Autumn Skies Are So Blue Share Flipboard Email Print Paul Zizka/All Canada Photos/Getty Images Science Weather & Climate Understanding Your Forecast Storms & Other Phenomena Chemistry Biology Physics Geology Astronomy By Tiffany Means Meteorology Expert B.S., Atmospheric Sciences and Meteorology, University of North Carolina Tiffany Means is a meteorologist and member of the American Meteorological Society who has worked for CNN, the National Oceanic and Atmospheric Administration, and more. our editorial process Tiffany Means Updated July 30, 2019 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.