# Really confused about skylight polarization

• jangheej
In summary, the degree of polarization is maximum when looking at 90 degrees to the sun, but it is not 100%. There are also singularities in the degree of 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?

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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.

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...

jangheej said:
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)

jangheej said:
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?

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

## 1. What is skylight polarization?

Skylight polarization refers to the phenomenon where light from the sun or sky becomes polarized as it passes through the Earth's atmosphere. This means that the light waves align in a certain direction, which can affect how we perceive and interact with the light.

## 2. How does skylight polarization occur?

Skylight polarization occurs due to the scattering of sunlight by particles in the Earth's atmosphere, such as air molecules and dust. This scattering causes the light waves to align in a specific direction, resulting in polarized light.

## 3. Why is skylight polarization important?

Skylight polarization has important implications in many fields, including ecology, navigation, and astronomy. In ecology, it can affect how animals and plants perceive and respond to their environment. In navigation, it can help animals and humans to determine direction and orientation. In astronomy, it can help us to better understand the properties of light and the universe.

## 4. How can I observe skylight polarization?

Skylight polarization can be observed through various methods, such as using a polarizing filter or polarimeter to measure the polarization of light. It can also be observed through certain natural phenomena, such as the polarization of light in the sky during a rainbow or in reflections off of water.

## 5. What are some real-world applications of skylight polarization?

Skylight polarization has many practical applications, including in photography, where polarizing filters can be used to reduce glare and improve image contrast. It is also used in polarized sunglasses to reduce glare and improve visual clarity. In addition, skylight polarization is used in satellite imaging to enhance images and in polarized light microscopy to study biological and geological samples.