There’s no better time for a road trip than summer. But while they always lead us to exciting destinations, the journey itself can be quite laborious and hot. For hours, you may be stuck in a car, mindlessly looking out of the window, dozing off, or even driving. Sometimes in the heat of the day, a shimmery haze appears on the horizon as if water or even oil have been spilled all over. Yet there’s not a single cloud in the sky, and once you approach and drive past, the highway is as dry as it has been and the puddle has moved on.
Everyone who has observed asphalt in the summer has seen this phenomenon. It is called heat haze, an inferior mirage since it appears under the real object.
But how exactly does it form?
Under the sun, asphalt is much akin to a stove top, radiating heat and even capable of frying eggs if necessary. It turns the air drifting over it into a nice warm blanket that clings to the ground.
Like any optical mirages, the vision is caused by the way light travels through substances. Different media, including different atmospheric conditions, allow and bend light differently.
When it hits this border between the hot air of the asphalt and the cooler air above, the rays are refracted. What we see is the sky lying on the road because of how light is bent and redirected but our brain interprets it as water. Due to this refraction we may also see cars as if reflected in the surface underneath strengthening the illusion of water.
This phenomenon is also why we see oases and mirages in the desert.
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