Why Is The Autumn Sky So Blue?


Why Is The Autumn Sky So Blue?

Why Is The Autumn Sky So Blue?
Why Is The Autumn Sky So Blue? – image via mnn.com

Have you ever noticed just how intensely blue the autumn sky is? Of course you have, and if you haven’t, then you should really get out of the house more. Now, the question is why? Why is the autumn sky so blue? Well, if you’ve come to read this article, then you must really want to know, which is great. And as you might have suspected by now, there are some scientific reasons behind it. So, what are they?

Lower Humidity

The first reason is that autumn has a lower humidity in the air than the other seasons. Fall is known to have a pleasant weather, especially when it’s closer to summer than winter. The temperatures aren’t as high and there’s less relative humidity in the atmosphere. And as some of us know, cooler air can’t carry as much moisture as warm air can.

And if there’s a lower humidity, that means that there are fewer clouds in the sky. And with fewer clouds and haze to cover the sky, its blue appears to be purer an more intense – making the sky to appear more open as a result.

The Sun is Lower

As time marches on and goes from summer to winter, the planet shifts on its axis a bit, making the sun appear lower in the sky than it does during the summer months. With the Sun no longer directly overhead, makes much of the sky be further away from its glare if you will. Similarly to how you would point a flashlight directly onto a surface and it makes it harder to see, somewhat the same principle is at work here.

The Rayleigh scattering directs more blue light towards our eyes, while the indirect sunlight decreases the incoming levels of red and green – resulting in a more intense blue than in other seasons.

Autumn Leaves

This last one might come as a surprise to some, but contrast also plays an important part here. In other words, the many shades of red, yellow, orange, gold, and brown actually help give the sky its bright blue colour.

Colour theory tells us that primary colours such as blue, become more brilliant if they’re located next to its complementary colour. When looking at a colour wheel, we can see that blue and violet are directly opposed to yellow and orange. This means that seeing the clear blue sky just over a forest of changing leaves, makes the sky look that more intense.

The colour wheel – image via hgtv.com