A shadow is caused when an object blocks light. Shade is actually a large shadow, often caused by blockage from a tree, building or another large object. Shade is often cool because the infrared rays from the sun that cause heat are also blocked. Most types of illumination are bright enough to cause shadows, including a full moon.
The majority of shadows are made of two parts called the umbra and the penumbra. The umbra is the area of maximum darkness where no light shines through. The penumbra is the area of medium darkness because some light is still not blocked. Some shadows do not have a penumbra, such as those that are caused by shining a light through a point source, such as a tiny hole in a piece of paper.
In an artistic setting, shadows can be used to improve a composition or set an atmosphere. For example, photographers use shadows to make aerial photographs look more three-dimensional. A solar eclipse is caused by the moon's shadow landing on the Earth. During a solar eclipse, scientists are able to perform unique studies on the sun.
It is possible to bend light waves, which may cause visual phenomena. When light waves move from the sky towards the ground, and then are bent by heated air, the result is an optical illusion called a mirage.