I am talking about the Northern hemisphere, specifically Europe. And it's true in every Europen country I've visited. The sky always seems to be paler in the Northern direction, compared to the Western/Eastern directions. Due South is even paler than the North due to the Sun being there during most the day of course. My question is why are East and West are darker shades when the sun isn't there, for example during midday? When the sun is still in the Eastern sky the West is very dark. When the sun goes to the Western part of the sky the East looks a darker shade of blue than the West and the North. And I'mn not talking about sunrises and sunsets. At the same time during midday when the Sun is shining in the South, the oppsosite direction (North) isn't as dark as East and West, it's quite a pale shade of blue.

Go to any European city during midday. The Southern portion of the sky with the sun will be the brightest hue of blues, it turns to deeper shades quite fast on the Eastern and Western parts of the sky. And when you look at the North the hue starts becomign paler again.

This 360 degree photo of Prague shows it best, the Northern potion of the sky is in the right and there's almost like a whitish hallo there, while the deeper blues in the East/West porions (maybe not true East/West) go closer to the Earth: enter image description here


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if I understand well your question there are two cases: a) midday: in Prague, Berlin etc the sun is in the south and the angle is the smallest one. (see the attachment)enter image description here In this case, the light of the sun has to cover less distance to reach the Earth. In other words, less scattering. Thus, it is more common for the light to go straight without scattering as direct flux.

b) other phases of the day. Thus, the angle is higher. The distance the light has to cover increases with the cosine. In this case, the light has to cover more distance and is more likely to be randomly scattered as it is scattered by the atoms in the atmosphere.

When the atmosphere is polluted, larger particles = Mie, there is no preference according to wavelength, so in very polluted atmosphere the sun more difficult to be seen.

Note that there are two kinds of scattering Mie and Rayleigh. Rayleigh scattering applies more for violet and blue and is the reason for the blue color of the sky.

But in other case further study of Rayleigh and Mie scattering will help you more (than me) to understand this phenomenon. Hope that helps


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