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Why Does It Look Like There’s Water on the Road When It’s Hot Outside?

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hot road mirage water illusion pavement vapor wet Water on the Road

Here’s why the road looks like it’s wet
Photo: via cc

As we’re in full swing of the summer heat, you’ve probably driven down the road recently and seen what appears to be pools of water glimmering on the pavement. Of course, even though it looks like there’s water puddled on the concrete, you know that once you reach the area, there isn’t actually any water on the road.

Ever wonder why this strange phenomenon happens? Here’s the science behind why the road looks wet on a hot summer day.

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Why the road reflects light like puddles of water do

You may have guessed that the appearance of fake water on the road ahead is some sort of mirage, and that’s correct. It’s the same thing that happens when people in the desert think they see water over a nearby sand dune.

This reflective illusion is caused by refraction. While light passes in a straight line through a medium of uniform density (like air), it “bends” (i.e. refracts) when it passes from one medium into another — like when you look through a glass of water. This is because light rays travel slower and at different angles through mediums of different densities, which means that even passing through areas of the same medium that have different densities can affect light’s path.

In the case of the “water on the road,” because the air directly above the road is hotter, it causes light rays from the sky to bend and wind up aiming at your pupils. Thus, you can’t see the road ahead and instead see wavy splotches of reflective surface instead — what would normally look like pools of water.

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Source: Mental Floss