A mirage is an optical illusion that has a scientific explanation. A common mirage is seeing a pool of water in a desert, which doesn’t really exist. This happens when light beams bend. In space, light travels fast because there is nothing slow it down. On Earth, light has to travel through the atmosphere, which slows it down. When light travels from cooler air to warmer air, it bends. This happens because there is something that is changing the speed at which the light is traveling. One part of the light wave changes speed just a split second before the other. That makes the light wave turn. Under certain conditions, usually on hot sunny days, light beams bend when they hit hot air close to the ground. Instead of reaching the ground they bounce up toward your eyes. What you see is a mirror image of something on the ground, a reflection that looks like a puddle.