Just as a wanderer in the desert can experience mirages, when light from remote objects is bent by the warm air hovering just above the sand, we may also see mirages in the Universe. The mirages we see with a modern telescope like the Hubble Space Telescope do not arise from oases, but instead from remote clusters of galaxies - huge concentrations of mass.

Credit: NASA, ESA, Andrew Fruchter (STScI), and the ERO team (STScI + ST-ECF)