A mirage is a phenomenon that is real and occurs regularly when there are events going on that can bend, or rerfract light waves. Mirages are visual images of objects far away that appear to be something other than what they really are. This is accomplished by the bending of light waves by interference from some other type of radiation from the electromagnetic spectrum. Mirages are real, they can be captured as video footage and replayed on video monitors.
Looming, on the other hand, is not real, and has to do with the brain's perception of an image as it is visually enlarged. The brain interprets the image becoming larger as the image or surface is getting closer, and orders the body to physiologically react to that apparent approach. As the name suggests, the image looms, or gets bigger, more imposing, as if it were literally right on top of you. This is an artifically produced perception of the central nervous system.