Distant Hill look Blue;Sunsets Red: Why?

If you look off into the distance, the hills on the horizon look blue-this is because the atmosphere tends to absorb the red light, leaving blue. But at sunset, the opposite occurs-the sky becomes red , and the sun appears red as well. Why is this?

This is due by a combination of contrast and the fact that that red light is absorbed by the atmosphere in the direction of the Sun. The only light reflected off of the facing sides of the hills is the blue light scattered still scattered from above. Since blue light appears brighter to the eye than red (and the sky in the background is very bright in the red spectrum) then the hills look blue.


The blue end of the spectrum of visible light is scattered by the atmosphere more than the red end, so when you look at the sun through a lot of atmosphere, you see more red than anything else, because the blue light is being scattered away before it gets to you.

When you look at the sky, or the atmosphere between you and the hills, it’s the scattered blue light you’re seeing - you don’t see so much of the red light, because that’s going straight on through and missing you.

You can replicate this effect yourself at home by means of a simple experiment; get a large transparent glass container, fill it almost full with water, then add a little milk and stir to mix.
Shine a flashlight through the mixture - when you look straight on at the beam shining toward your face, it will appear reddish or at least orangey. When you move around to the side so that you’re observing the beam traversing sideways through the liquid, it will look bluish.

That’s a great visual experiment!! I think I’ll suggest that one to some of my friends in the science part of the education program here. :slight_smile: