Originally posted by adeclerk
reply to post by Britx
You haven't noticed the blue sky? It's right above you, blue as ever. No changes here.
"right above you" is always where the sky is most blue, as there's far less particulates looking vertically than looking horizontally, and because the
white Mie scattering mostly projects away from from the sun.
This can lead to perceived changes in blue sky depending on where you live, and and then where you move to. If you live on the lower regions of the
south side of a valley in the northern hemisphere, then your average sky will be a LOT bluer than if you live on of the west side of a solitary hill.
Here's and extreme example. If you live in the Grand Canyon, then you'll be looking up a lot to see the sky, so it's going to seem bluer. It also
generally runs east-west, so on average you'll be at right angles to the sun. Hence any river rafting trip you take in the Grand Canyon is going to
give you bluer skies than normal.
You can see how the blue varies with direction in any 360 degree panorama:
Note the sky is bluest in the two regions that would be at right angles to the sun (assuming the sun is in the south here, the bluer regions are in
the east and west.
The north sky (where the clouds are) is also whiter (Mie also scatters backwards, and I suspect direct reflection may play a part).
And of course, it's whitest near the horizon in every direction.
So think about where you live when you question how blue the sky is. What direction are you looking in? Where is the sun? How high are you looking?
Can you see the horizon, or are there nearby hills?
And if you have memories of particularly blue skies, try to remember is any of this might have played a part in what you saw.
edit on 8-6-2011
by Uncinus because: added grand canyon pic
edit on 8-6-2011 by Uncinus because: (no reason given)