A Simple Way to Demonstrate and Explain Different Facets of Mirages

As intriguing optical phenomena that occur in nature, mirages are widely known and often mentioned in physics classes when introducing the basics of optics. In the atmosphere, a mirage occurs under the condition of vertical variations in air density, which are usually caused by a temperature gradient. The light rays are continuously refracted and follow a curved path when passing through the air, because the refractive index of air changes with its density. Hence, the image observed in an optical manner is displaced from the location of the object. An upward-shifted image is known as a superior mirage, whereas a downward-shifted one is known as an inferior mirage. There are several simple experiments that can create both superior and inferior mirages, using a non-uniform liquid solution to simulate the refractive index gradient in the air. These experiments not only demonstrate the curved paths of light rays, but also produce artificial multiple-image mirages. This paper introduces a simplified method of creating inferior mirages in a liquid solution. Using this method, we further demonstrate several different facets of mirages and explain their origins through computer simulations.