Folks

Maybe some people here can help. I have found out that some moonlight is polarized, but am trying to find out why. Can someone explain when moonlight is polarized, and how much it is and why?

Thanks!

No idea why but I was intrigued & google brought up this gem;

"Nature Magazine – July 2003

An African beetle relies on moonlight's polarisation to roll its dungball in a straight line, researchers have discovered.

Dacke and her colleagues discovered that beetles chart a straight course only on moonlit nights. Without the Moon, they meander randomly.

To test whether the beetles use light polarization, rather than the position of the Moon, to maintain a steady bearing, the researchers made sure the insects could not see the Moon. They then placed a polarizing filter over a ball-rolling beetle to turn its light through 90º.

The beetles made an abrupt turn either to the left or the right. This shows that the bugs use the sky's polarized moonlight to follow a straight course, but not to tell left from right."

google is your friend

Cheers Balls

I did google and find that thing about beetles.

That article only seems to mention sunlight. Is moonlight treated just as sunlight but reflected off the moon, i.e. the act of reflection has nothing to do with it?

I thought all reflected light was partially polarised, whether it's reflected off water, metal, erm…the moon.

And moonlight is just reflected sunlight, isn't it? Therefore it's partially polarised?
Can't explain why it's only 'some moonlight'.

Reflected light is generally polarised at certain angles. Which explains why you can see through the surface glare on water with polarised glasses. Though it's a long time since I did work on polarised light, so I'm dredging this from the depths of my mind.

Another fun polarised light fact is that measuring the rotation in the axis of polarisation is a good way to measure the concentration of sugar in a solution (and how it's done industrially).

I thought all reflected light was partially polarised, whether it's reflected off water, metal, erm…the moon.

so even reflections off cheese polarise the light?

now I have this picture of Simon Ralli only able to go in a straight line in moonlight :o) In fact he may be rolling dung…

sockpuppet. Spot on. In fact, cheese is the most heavily polarising substance known in the universe.

I once looked at a particularly large lump of Gruyere wearing polarising shades and the reflected light was so heavily polarised, I couldn't see the cheese. It was only my keen sense of smell that allowed me to determine it was in fact cheese.

It's actually a little known fact that the Hubble telescope is lined with slices of that processed burger cheese to polarise any stray light before it hits the mirror.