Imagine you're in the desert. You're lost. You've been walking
for hours. You've run out of water. On the horizon, you see a
giant, shimmering puddle of water. "Yippeeeeeeeeee", you shout.
You're saved!
But...it's not a puddle of water. It's a
mirage.
Mirages are optical illusions that have fooled many thirsty
explorers.
How do mirages form?
Normally, light waves from the sun travel straight through the
atmosphere to your eye. But, light travels at different speeds
through hot air and cold air.
Mirages happen when the ground is very hot and the air is cool.
The hot ground warms a layer of air just above the ground.
When the light moves through the cold air and into the layer of
hot air it is refracted (bent).
A layer of very warm air near the ground refracts the light from
the sky nearly into a U-shaped bend. Our brain thinks the light has
travelled in a straight line.
Our brain doesn't see the image as bent light from the sky.
Instead, our brain thinks the light must have come from something
on the ground.
You can even see mirages in the UK. Have you ever seen a wet
looking shimmer above tarmac on a hot day? That's the beginning of
a mirage.