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xkcd on Rayleigh scattering | 179 comments | Create New Account
Comments belong to whoever posts them. Please notify us of inappropriate comments.
xkcd on Rayleigh scattering
Authored by: bugstomper on Saturday, March 16 2013 @ 09:38 PM EDT
Ian Al,

It's because a mirror does not reverse right and left, it reverses front and
back. Light hits the mirror and reverses direction as it comes back to you.

Print letters in black marker on a piece of paper and hold it up to a light with
the side with the print facing away from you so the light makes the paper
translucent and you can see the letters through the paper, from the back. The
letters will be in "mirror writing". A mirror shows you how something
looks from the back except that what is farther from you occludes what is
closer, back and front reversed.

Why does it appear that right and left is reversed? Notice what is to your
right. Now turn around. It is now on your left. Why does right and left reverse
when you turn around but up and down not reverse? Because you don't stand on
your head when you turn around. If you bend over and stand on your head you can
see what was behind you with up and down reversed but right and left not
reversed. The experiment is left as a yoga exercise for the reader.

By the way, I think that the explanation as to why the sky isn't violet is the
more interesting of the two questions raised by that comic. If the reason the
sky is blue is because Rayleigh scattering spreads out the higher frequencies
more, shouldn't that make the sky colored at the highest frequencies we can see
in the rainbow? Violet light is there in the sunlight as we can clearly see when
there is a rainbow, so why isn't that the color of the sky?

The answer to that has to do with some details of our color perception and may
actually have an evolutionary benefit.

[ Reply to This | Parent | # ]

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