penumbra and umbra example

29 Sep: Contact Shadows & Cast Shadows: A myth

Cast shadows, we are told, are the sharp shadows you can see cast by an object that is lit by a light source like a sun or light-bulb while contact shadows, apparently, are those kind of indistinguishable darkenings without a discernible edge that seem to appear as an object gets close to, and touches, a surface, like a car tire on the road on a cloudy day.