Mirages may be closer to hom than you think

By Al Lowe
Contributor

When you hear the word 'mirage', you probably think of travellers in the desert, intensely hot, dry and thirsty. Suddenly, they see a vision in the sky - an oasis with green trees and cool waters.
Well, that mirage really does happen sometimes, but there are many others closer to home. Some of them you see nearly every day.
A mirage is an optical illusion. You see something which really isn't there, or see something in the wrong place. Some mirages, or optical illusions, are caused by the reflection of light, and others by the bending, or refraction of light. Let us look at two of these mirages caused by bending of light.
First of all, when does light bend? When it goes into a substance of different density. For instance, when light goes from air into water or glass, it bends. Did you ever notice a stick which was partly in the water? It looks as though it is crooked. It appears to be bent at the surface of the water. But it isn't the stick which is bent. It is the rays of light which bend when they enter or leave the water.
For the first mirage, put a coin in a tall glass of water. Look down into the water from above. Put you finger on the side of the glass where the coin appears to be. Aha! Your finger is above the coin, isn't it? The light bends a little as it leaves the water, and that makes the coin appear to be above where it really is.
Suppose you wanted to shoot a fish in the water. Where would you aim? You would have to aim below where the fish appears to be. Just like the coin in the glass, the fish is deeper than it looks. If you aimed at where you think it is, your bullet would go right over its back.
Another mirage is even more common. It happens every day at sunset. Light from the sun travels nearly 90 million miles to get here, through empty space. When it gets to the earth's atmosphere, it is entering air, which is much more dense than outer space - there is more material in it. And so it bends a little. Because of this bending, the sun is not where it appears to be.
It may come as quite a surprise to you to find out that the sun is really below the horizon for several minutes before it 'sets' in the west. The bending of the light makes it appear to be still up in the sky, when it is really below the curve of the earth.
There are many more common mirages, or optical illusions. Every time you use a magnifying glass, or a miroscope, or a shaving mirror, or a rearview mirror, and a host of other things, you are seeing images which are not really there.
And those are mirages.