In fact, mirages are very common. For example, unless obscured by clouds or topography, the image we see of the sun just rising or setting on the horizon is a mirage, for the sun is actually below the line of direct sight to the horizon. In the atmosphere, mirages are categorized as either an inferior mirage or a superior mirage . We most often see the inferior mirage. Nowadays this mirage is so common we almost don't think about it.
Inferior mirages occur when the air close to the surface is much warmer than that above it.
Thus the desert mirage is an inferior mirage. Skylight passing through this air is bent by refraction so that it appears to be coming from a source below the horizon. The superior mirage forms above the horizon and is seen where warm air overlies cold air, a condition known as a temperature inversion . Superior mirages can be quite common over cold water and snow surfaces. Here in Victoria, British Columbia, the colder waters surrounding Vancouver Island provide ideal conditions for superior mirage viewing.