# Question about polarization of light by scattering in the atmosphere

• I
• annamal

#### annamal

My book says:

I don't understand why the bottom eye only sees the horizontal red arrow and not the other angles (black arrows)

Delta2

The diagram is very confusing. Let's call the direction of propagation z, x is the plane of the paper and y is normal to the paper.
A component of the unpolarised source lying in the y direction will cause an electron in the scatterer to vibrate also in the y direction. It will then radiate all round in the x plane, and you will see it from the bottom location.

However, if the unpolarised source radiates a wave polarised in the x direction, it will cause an electron in the scatterer to vibrate in the x direction also. The electron is then end-on to the bottom observer and does not radiate in that direction.
So the bottom observer sees only those waves from the source having components in the y direction, and which are therefore polarised.

Delta2
Tested experimentally now with polarization filter on a blue sky. Effect is real - visible as fuzzy blackening in the arc roughly perpendicular to the direction to Sun.

Delta2 and berkeman
Remember the plane of polarisation aligns with the circumference of the arc, so rotates as you go around this halo.

The diagram is very confusing. Let's call the direction of propagation z, x is the plane of the paper and y is normal to the paper.
A component of the unpolarised source lying in the y direction will cause an electron in the scatterer to vibrate also in the y direction. It will then radiate all round in the x plane, and you will see it from the bottom location.
What is the scatterer?
However, if the unpolarised source radiates a wave polarised in the x direction, it will cause an electron in the scatterer to vibrate in the x direction also. The electron is then end-on to the bottom observer and does not radiate in that direction.
How do you radiate a wave polarized in the x direction?
So the bottom observer sees only those waves from the source having components in the y direction, and which are therefore polarised.

In reply to post #5, the scatterers in the atmosphere are particles of dust and gas molecules.
Waves polarised in the x direction will be present in "unpolarised" sunlight - it is when the electrons vibrate in the plane of the paper.

The diagram is very confusing. Let's call the direction of propagation z, x is the plane of the paper and y is normal to the paper.
A component of the unpolarised source lying in the y direction will cause an electron in the scatterer to vibrate also in the y direction. It will then radiate all round in the x plane, and you will see it from the bottom location.
What do you mean by "It will then radiate all round in the x plane"

If electrons in the scatterer vibrate normal to the paper, they will radiate in all directions in the plane of the paper. It is similar to the radiation from a vertical antenna.