1. Jun 2, 2010

### GreatEscapist

Today it got kinda hot, and while I was in the car, I noticed those stupid mirror-mirages-things on the road, where it reflects everything.

I know that it does that because it is hot, but can someone explain the complicated version of why it looks like a mirror puddle?

2. Jun 2, 2010

### Lambduh

Probably because you're seeing a reflection of the blue sky. As you said the reason that you actually see the sky/horizon/whatever is that the air near the hot black road heats up and acts as a mirror. As air heats up the index of refraction changes. A gradient temperature near the road produces a gradual change in index of refraction as light approaches the road. This is what causes light to bend back up so that you see an image of the sky above.

As temperature increases the index of refraction increases as well. Snell's Law tells us:

$$n_1 \ \sin \theta_1 = n_2 \ \sin \theta_2$$

so basically going to a higher index of refraction bends light towards the normal. In this case away from the road and up towards your eye.

http://en.wikipedia.org/wiki/Refraction

For a more thorough explanation:

http://en.wikipedia.org/wiki/Mirage

Other than that I'm not sure what you might mean by "mirror puddle"

Last edited: Jun 2, 2010
3. Jun 2, 2010

### GreatEscapist

Lol. I'm not a great describer.

I see the cars in front of me, and the trees, and it looks like puddles. Like water. Except they reflect.

I understand it's because it is hot. But why does hot=acts like a mirror?

4. Jun 2, 2010

### Lambduh

Woops, was in the process of editing my post above to make it more clear. Post again if you still have questions.

5. Jun 2, 2010

### GreatEscapist

Oh. That makes sense.

I love it when there's formulas for things. It makes my mind so much more at ease.

6. Jun 2, 2010

### cragar

Ok i get that hotter air is less dense , but when light goes from hot air to colder air we are dealing with the same atoms it is just that the photon will have less collisions , why would the angle of re-emission change for the photon just because it is having less or more collisions in the medium. As the photon gets absorbed and re-emitted , why would this cause refraction just because the atoms are close together and then far apart how does this change the angle that the photon gets re-emitted out of the atom .