The Road That Looks Wet

Written by Studio AM.

On a hot day, a distant road may appear to hold a shining pool. As a driver approaches, the water seems to retreat. The surface is dry. This common mirage is an image produced when light bends through layers of air at different temperatures.

Sun-warmed pavement heats the air directly above it. That air can be much warmer and less dense than air a little higher. Light from the bright sky travels downward through the changing layers, bending gradually. Near the road, its path may curve upward toward an observer's eyes.

The brain usually treats arriving light as if it traveled along a straight line. Tracing the upward ray backward places its apparent source below, near the road. The result can resemble sky reflected from water, including a wavering patch that changes as hot air moves.

The mirage is real as an optical event, but the apparent pool is not a physical object on the pavement. It does not mark a wet patch that keeps escaping. It reveals how the atmosphere can redirect information before light reaches an observer.

Questions

Choose an answer. The explanation appears after you answer.

  1. Question 1 of 4

    What is the main idea of the passage?

  2. Question 2 of 4

    Why does the apparent water look like part of the sky?

  3. Question 3 of 4

    What does “retreat” mean in the opening paragraph?

  4. Question 4 of 4

    Which air is described as less dense?

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