This blog post explores the principle of how light refraction creates mirages in deserts and polar regions. Discover the science behind how mirages form.
A mirage is a phenomenon where an object that isn’t actually present appears as if it were there. However, a mirage is not an illusion or trickery; it is a phenomenon where the original object appears in a different location due to temperature differences in the air layers. This phenomenon is a very interesting topic in physics and can be described as a natural ‘optical illusion’ caused by the refraction of light and differences in density. A mirage is not a simple visual error but the result of scientific laws created by the natural environment. Cold air layers have higher density, while warm air layers have lower density. This density difference alters the time light takes to pass through the air; higher density means longer travel time. As light passes through these air layers, it refracts when crossing the boundary surfaces of differing densities. Therefore, mirages are easily observed in deserts or polar regions where the temperature difference between the surface air and the air above is significant.
This natural phenomenon has provided people with a mysterious experience for a long time. For example, travelers crossing deserts in ancient times often witnessed mirages and mistakenly believed they were oases or villages appearing. This is a good example of how realistically mirages can appear visually. During hot summers, the desert surface easily absorbs sunlight and heats up, causing the air near the surface to warm more readily than the air above it. Hot air has a lower density than cold air, and this density difference causes light to refract. Suppose there is a single tree in the desert. Some light rays originating from the tree’s upper part travel straight and reach the human eye directly, so we see the tree standing upright. However, some of these light rays, as they travel downward, pass through denser layers of air and continue to refract, rising back upward. Light rays originating from the tree’s lower part also continue to refract, rising higher. Because the positions of these two light rays are reversed, the tree appears to stand upside down to the observer. This is called a ‘lower mirage’. Therefore, when viewed from a distance, the image of the upright tree and the inverted tree beneath it are seen simultaneously.
Mirage phenomena also occur in extremely cold regions. The air near the snow-covered surface in polar regions is always much colder than the air above it. The density of the cold air layer is high, while the density of the warm air layer is low. Due to this density difference, light refracts toward the denser surface layer and enters our eyes. Consequently, mountain peaks in polar regions appear higher than they actually are. This phenomenon is called an ‘upper mirage’.
Mirage conditions vary widely. For instance, mirages can also be observed at beaches. When seawater near the shoreline lies at the boundary between cool and warm air, objects near the horizon may appear distorted. This often makes ships seem to float in mid-air or causes the shoreline’s appearance to appear greatly distorted. On hot summer afternoons, the surface temperature rises easily. Driving over heated asphalt roads can sometimes make the road surface ahead appear as if there are puddles of water. However, as the car approaches, these puddles quickly disappear, only to reappear a short distance further ahead. This phenomenon occurs because the temperature difference between the surface and the air above it causes light from the sky to refract, entering our eyes. Heat haze is also a type of mirage. On spring days when the weather suddenly warms, heated air near the ground rises and falls, causing irregular density changes. These changes create differences in light refraction, resulting in heat haze. In this case, the object’s position remains unchanged, but the haze makes it appear to shimmer in place.
