Replies

Imagine a smoke column - a wide one, but one that is kind of ‘thin’ - and the sun is behind or to the side of the smoke column.

Imagine again that you have a mirror.

If you use the mirror to ‘shine’ sunlight into he smoke column you would see?

A square. You have seen the displays that project an image onto a water vapor - yes?

If the smoke column has a white object in ‘front’ of it, with square corners or straight lines, the light would reflect sunlight onto the smoke column. And the light would appear to be a straight line in the smoke.

Or not.