Mirages, Rainbows, Colours and Film Interference

A mirage is just an image that we think we see but we in fact don't. Mirages are caused predominantly by air temperature differences near the ground. Air has different refractive indexes at different temperatures so hot air and cold air reflect light by different amounts. It can be bent either upwards towards the sky or downwards towards the ground depending on the temperature gradient whether it gets hotter going up or colder going up. The resolving power of sort of real telescopes is not limited by that because it's pretty easy to make a telescope that magnifies a lot, what's hard is to make one that doesn't have lots of aberration.