A mirage occurs on very hot days when a layer of hot, low density air lies
on the ground. Light from the sky will be totally internally reflected at this layer and so you see
what looks like a pool of water - it's actually a reflection of the sky.
You may often see a
shimmering layer of reflecting air on a road on a very hot day – that is a mirage.
There
is no sharp boundary between hot and cooler air and so the refraction is gradual.
Mirages also occur
in very cold countries. See if you can explain why.
In the next diagram the mirage appears in the
sky and the polar bear seems to be flying upside down!
