Where there is no light there is darkness, we call this a shadow. In fact at night we are in the
shadow of the Earth.
You can see from the two diagrams that there are two types of
shadow; a crisp edged one formed by a point source of light and a rather more fuzzy one that
is formed by a larger source.
The region of deep, total shadow is called the
UMBRA and the region of partial shadow is called the PENUMBRA. The umbra is a region where no light can get to while the penumbra is a region where some light can reach.
You can use shadow
effects in photography to give the right atmosphere to a picture.
Shadows also explain lunar and solar
eclipses and you can find out more about these in the section on astronomy.