Mirages are an optical phenomenon – they aren’t what you see when you’re dying of thirst while walking across the desert. That’s more likely a hallucination. Mirages can actually be photographed because it is a case of light rays being bent to form a false image that we see.
Sometimes there can be a big difference in the temperature of different layers of air. When light rays pass from the cold layer to the hot layer, or vice versa, the light ray gets bent and the light now travels in a different direction to where it was originally going. When these bent light rays hit the back of our eye (our retina) or gets caught on camera, it’s hard to tell where the light rays originally came from. They have produced an image that is not necessarily there.
Yup – it’s “refraction”. The light rays bend. Light’s weird. I think typically with a mirage you see the sky where the hot road should be, right, so it looks like there’s water? The light from the sky near the horizon, rather than hitting the road up ahead, gets bent by the hot air near the road and shoots into your eye. So you see sky where road should be. That air is less dense near the road surface (it has a lower “refractive index”, and this bends it. How light travels depends on what it’s travelling in. You know this because when you put your hand in water it looks like your hand and your arm don’t match up any more. The light changes direction when it enters and leaves the water. A mirage is the same thing, but the bending happens because air temperatures vary.
[Cooler – light also gets bent by gravity. A big star can bend light around it. That’s super weird and is called “gravitational lensing” and was a big bit of evidence for the theory of relativity, which you’ll read about if you read books on physics. Anyway, if anyone ever tells you light goes in a straight line, laugh loudly.]
I used to think mirages were only something that was only in stories. I just never saw them. Of course this all changed when my family went on a driving holiday one summer. That was the first time that I saw a large lake on the horizon that no matter how far my dad drove the car, we never managed to reach it.
The reason for this is because the large lake was caused by light at the horizon never quite reaches the road to reflect off it before reaching our eyes. The light from the sky is being bent by a very hot layer of air near the road. So what we end up seeing looks like the reflection of the sky.
It’s a little hard explaining this without drawing a diagram so I’ve found a 60 second video that explains this with diagrams. http://vimeo.com/11121424
When air heats up, it expands. When there is hot air next to cold air it can act like a lens to bend light. But the catch is that it does not always bend light.
Glass can bend light. But windows are made so that they do not bend light. Specially-shaped glass act as lenses. So whether of not light is (or is not) bent depends on the shape.
So when the volumes of hot and cold air just happen to have the right shapes, then light is bent and we see something that LOOKS as if it is in a different place. Where we see it (the mirage or image) is not really there. It is really somewhere else because the light has been bent.
Mirages are an optical phenomenon – they aren’t what you see when you’re dying of thirst while walking across the desert. That’s more likely a hallucination. Mirages can actually be photographed because it is a case of light rays being bent to form a false image that we see.
Sometimes there can be a big difference in the temperature of different layers of air. When light rays pass from the cold layer to the hot layer, or vice versa, the light ray gets bent and the light now travels in a different direction to where it was originally going. When these bent light rays hit the back of our eye (our retina) or gets caught on camera, it’s hard to tell where the light rays originally came from. They have produced an image that is not necessarily there.
1
Yup – it’s “refraction”. The light rays bend. Light’s weird. I think typically with a mirage you see the sky where the hot road should be, right, so it looks like there’s water? The light from the sky near the horizon, rather than hitting the road up ahead, gets bent by the hot air near the road and shoots into your eye. So you see sky where road should be. That air is less dense near the road surface (it has a lower “refractive index”, and this bends it. How light travels depends on what it’s travelling in. You know this because when you put your hand in water it looks like your hand and your arm don’t match up any more. The light changes direction when it enters and leaves the water. A mirage is the same thing, but the bending happens because air temperatures vary.
[Cooler – light also gets bent by gravity. A big star can bend light around it. That’s super weird and is called “gravitational lensing” and was a big bit of evidence for the theory of relativity, which you’ll read about if you read books on physics. Anyway, if anyone ever tells you light goes in a straight line, laugh loudly.]
1
I used to think mirages were only something that was only in stories. I just never saw them. Of course this all changed when my family went on a driving holiday one summer. That was the first time that I saw a large lake on the horizon that no matter how far my dad drove the car, we never managed to reach it.
The reason for this is because the large lake was caused by light at the horizon never quite reaches the road to reflect off it before reaching our eyes. The light from the sky is being bent by a very hot layer of air near the road. So what we end up seeing looks like the reflection of the sky.
It’s a little hard explaining this without drawing a diagram so I’ve found a 60 second video that explains this with diagrams. http://vimeo.com/11121424
0
When air heats up, it expands. When there is hot air next to cold air it can act like a lens to bend light. But the catch is that it does not always bend light.
Glass can bend light. But windows are made so that they do not bend light. Specially-shaped glass act as lenses. So whether of not light is (or is not) bent depends on the shape.
So when the volumes of hot and cold air just happen to have the right shapes, then light is bent and we see something that LOOKS as if it is in a different place. Where we see it (the mirage or image) is not really there. It is really somewhere else because the light has been bent.
0