Really confused about skylight polarization

[jangheej]

I learned that the light is 100% linearly polarized when one looks at the angle shown in pic1.

But when taking a photo of a blue sky and also in polarization navigation, it says that we look at the direction of 90 angle from the sun ray cos it's the region of maximum polarization. (pic 2)

But if what i learned was right (and I am quite sure) then doesn't it have to be like pic3?

help me please!

 

[cjl]

You have the right idea, but the scale of the image is wrong. The Earth's atmosphere is very, very thin compared to the size of the earth, and the sun is very, very far away compared to the size of the earth. As a result, the line of sight from you to the sky in the third image should be much shorter, and the sun should be much farther away. If you draw a few more cases with varying geometry, you should see that as the sun moves farther away and your line of sight becomes shorter, the condition approaches the one in your second drawing.

 

[jangheej]

but if the scale is what matters, then that means it doesn't matter which way you look at, doesn't it?
assume that the sun is very large and far away and the line of sight is very short as you said - then that means regardless of which region of the sky you look at, the angle between the sun ray and you will always be perpendicular...

 

[cjl]

but if the scale is what matters, then that means it doesn't matter which way you look at, doesn't it?
assume that the sun is very large and far away and the line of sight is very short as you said - then that means regardless of which region of the sky you look at, the angle between the sun ray and you will always be perpendicular...

No it doesn't. If you look towards the sun for example, the angle will be zero. If you look directly away from the sun, the angle will be 180. It's only when you're looking at a right angle to the sun that it will be perpendicular.

(Also, note that I didn't say the sun was very large. You can still consider the sun as a point source for this example)

 

[Andy Resnick]

I learned that the light is 100% linearly polarized when one looks at the angle shown in pic1.

But when taking a photo of a blue sky and also in polarization navigation, it says that we look at the direction of 90 angle from the sun ray cos it's the region of maximum polarization. (pic 2)

But if what i learned was right (and I am quite sure) then doesn't it have to be like pic3?

help me please!

The degree of polarization is a maximum when you are looking at 90 degrees to the sun; but it's not 100%.

http://www.polarization.com/sky/sky.html

There are also zeros (singularities) in the degree of polarization:

http://iopscience.iop.org/1367-2630/6/1/162/fulltext