Weather Wise Kids: What causes a mirage on hot days?

I am sure many people have seen exactly what you are talking about. You are driving down the highway on a hot day and small circles that look like puddles of water appear in the road. If you’re like me and grew up watching Rugrats, when you think of mirage you think of Chuckie in the desert.

The type of mirage Chuckie sees is called heat haze. Heat haze or heat shimmer happens when you are looking at an object through a layer of heated air. Most of the time this happens when you are looking through the exhaust gases produced by airplane engines or looking at an object across hot asphalt.

When a road is heated by the sun, the air closest to the road becomes hotter than the air just above it. This variation between the hot air at the surface of the road and the denser cooler air above produces the blurred shimmering effect you are seeing.  When light passes from hot to cold air, it’s refracted, or changes direction. It’s the same illusions you see when you put a pencil in a cup of water.


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