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Re: Cat's eyes



At 11:29 PM 9/2/00 -0400, Ludwik Kowalski wrote:

The
impression is that light from the kitchen is somehow
"reflected" from my eyes toward the cat and causes
them to shine. Why do I see the shining cats eyes only
when my eyes are sidewise illuminated by the kitchen
light?

The phenomenon is so well known that the term "cat's eye" applies not just
to cats but any retroreflector. It is implemented in cats as a lens with a
mirror in the focal plane. (Trace a few rays for yourself to see how this
works.)

The only light that you will see retroreflected is light that comes from
your face (or from something near thereto as seen from the cat's point of
view). Anything that shades your face and/or blocks light coming from
behind your ear will cut down the retroreflected signal.

===============

As to why there's a mirror in the eyeball, see _The Feynman Lectures on
Physics_ volume 1 chapter 35. (BTW contrary to what RPF says on page 35-1,
the fovea is much smaller than the macula.)

A retroreflector can also be implemented as a corner cube.