Puzzle 002
Draw on and cut out of stiff cardboard an ellipse and hold it in direct sunlight. The shadow of this ellipse appears to be another ellipse, regardless of how you hold it. This is not true for, say a square, which casts not only square but also rectangular, paralellogram, or rhomboid shadows, nor for, say a circle, which casts not only circular but also elliptical shadows.
Is it always true that the shadow of any (2-dimensional) ellipse cast on any (2-dimensional) surface is another (2-dimensional) ellipse, or does it only appear that way most of the time but not true in general, in which case, when is it true?
In case you are curious, the above fact about an ellipse is possibly the key to a solution to a mathematics problem that underlies absolutely unbreakable un-eavedroppable quantum encryption, transmission, and decryption of information.
Submit your proof to zoonspuzzle@nysf.com.
