Atmospheric Refraction is light being refracted in the air. One cool example of this is the mirage. When it is really hot outside, there is a very hot layer of air close to the ground. Molecules are father apart in hot hot air, so light travels faster in the warmer air. The gradual bending of the light rays is caused by the waves speeding up. This produces an image.

For example, sometimes while driving down a hot road, one may notice that the ground appears to be wet. It is really not wet, it is actually the light from the sky being refracted throught the hot layer of air.

You can see sample pictures of a mirage on the road at: http://www.weather-photography.com/Photos/gallery.php?cat=optics&subcat=mirages_inferior_road