Seeing things that aren’t there
Can a lake vanish? A few minutes ago you saw cool water shimmering just
up the road ahead of the car. But now all you see is miles of hot paved
highway. Where is the lake?
The disappearing lake is a mirage (muh [rahzh)]{.smallcaps}—something
that isn’t where it seems to be. The mirage is made by light reflected
from something far away. You can see a mirage only when there are layers
of cool air and warm air close to the earth.
Light usually travels in a straight line. But when light passes through
layers of warm and cool air, it behaves differently. The warm and cool
layers act like a lens. They bend the light.
If the bottom layer of air is warm, the mirage will be close to the
earth. But if the bottom layer is cold, the light will bend the other
way. The mirage will be high up—it may even seem to float in the air!
A mirage can come from surprising places. A \”lake” may be light waves
from far-off clouds. A rocky \”island” may be light waves from a distant
mountaintop. People at sea have even spotted \”ghost ships” floating
upside down in the sky—mirages of real ships far away on another part
of the ocean. And in the Strait of Messina, off the coast of
Sicily, an \”enchanted city” sometimes appears. It seems to be floating
in the water!
You can never reach a mirage, because what you see isn’t really there.
But the light waves you see are real. If you have a camera, you can
take a picture of the mirage. The camera will \”see” the light waves
just as you do—and you will have a picture of the thing that isn’t
there!
The water in this picture is real, but the sailboat and its reflection
are both mirages.
