My daughter Maya was not sure what I was doing but I promised here a stawberry sunday if she held still. The picture does not show the concept of umbra & penumbra but here is a definition that might help. ( note, blog would not let me download some nice animations that gave some examples of these concepts - please advise)
Umbra and penumbra from an extended source. You may have noticed that shadows are often fuzzy, particularly when the surface on which the shadow lies is far from the object casting the shadow. This fuzziness is because no light source is only a point in space. All sources have some geometrical size. Thus, light from one edge of the source is not quite parallel to light from the other edge.
The evenly dark part of a shadow is called the umbra. The fuzzy part between the dark and the light is called the penumbra.
If one is in the umbra of an object, the light source is completely obscured. If one is in the penumbra, the source is only partially obscured, to a greater or lesser degree as one moves through the penumbra.
The umbra of a shadow is not absolutely black because there is always scattered light that makes its way into it. In the case of sunlight, the scattered light is mostly bluish skylight, so shadows are bluer than normal.
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