Re: [Phys-l] Interesting Shadows

[John Denker <jsd@av8n.com>]

On 02/22/2011 03:47 PM, chuck britton wrote:

> A (perhaps) related question has to do with the shadow that an 
> airplane casts on the ground.
>
> Is it precisely the same size as the plane? or slightly larger, or 
> slightly smaller?

The umbra is always smaller, and the penumbra is always
larger.

> (or all of the above ;-) )

Two out of three.  I don't see how it could be the same size,
except in the case of zero distance, and in that case you
have a hard time seeing the shadow anyway.  Or unless you
have a cleverly contrived artificial light source (very
much smaller than the sun).