A superior mirage occurs when the air below the line of sight is colder than the air above it. Heat haze is not related to the atmospheric phenomenon of haze.Ī superior mirage is one in which the mirage image appears to be located above the real object. The illusion moves into the distance as the observer approaches the miraged object giving one the same effect as approaching a rainbow. This might appear as a pool of liquid (usually water, but possibly others, such as oil) on the road, as some types of liquid also reflect the sky. Light from the sky at a shallow angle to the road is refracted by the index gradient, making it appear as if the sky is reflected by the road's surface. This produces a blurred shimmering effect, which hinders the ability to resolve the image and increases when the image is magnified through a telescope or telephoto lens. Both tarmac and sand can become very hot when exposed to the sun, easily being more than 10 ☌ (18 ☏) higher than the air a meter (3.3 feet) above, enough to make conditions suitable to cause the mirage.Ĭonvection causes the temperature of the air to vary, and the variation between the hot air at the surface of the road and the denser cool air above it causes a gradient in the refractive index of the air. It also occurs in deserts in that case, it is referred to as a "desert mirage".
When appearing on roads due to the hot asphalt, it is often referred to as a "highway mirage". Common instances when heat haze occurs include images of objects viewed across asphalt concrete (also known as tarmac) roads and over masonry rooftops on hot days, above and behind fire (as in burning candles, patio heaters, and campfires), and through exhaust gases from jet engines. Heat haze, also called heat shimmer, refers to the inferior mirage observed when viewing objects through a mass of heated air. See also: Schlieren, Twinkling, and Astronomical seeing In any case, mirages are usually not larger than about half a degree high (roughly the angular diameter of the Sun and Moon) and are from objects between dozens of meters and a few kilometers away. If several temperature layers are present, several mirages may mix, perhaps causing double images. A combination of vibration and extension are also possible. The image will be distorted accordingly it may vibrate or be stretched vertically ( towering) or compressed vertically ( stooping). Since warmer air rises while cooler air (being denser) sinks, the layers will mix, causing turbulence. While the aero-dynamics are highly active, the image of the inferior mirage is stable unlike the fata morgana which can change within seconds. The image is usually upside-down, enhancing the illusion that the sky image seen in the distance is a specular reflection on a puddle of water or oil acting as a mirror. Therefore, rays coming from the top of the object will arrive lower than those from the bottom. Light rays coming from a particular distant object all travel through nearly the same layers of air, and all are refracted at about the same angle.
Superior mirage Patch#
The mirage causes the observer to see a bright and bluish patch on the ground.
The real object in an inferior mirage is the (blue) sky or any distant (therefore bluish) object in that same direction. In an inferior mirage, the mirage image appears below the real object. For example, inferior images on land are very easily mistaken for the reflections from a small body of water.Ī schematic of an inferior mirage, showing a) the unrefracted line of sight, b) the refracted line of sight and c) the apparent position of the refracted image. What the image appears to represent, however, is determined by the interpretive faculties of the human mind. In contrast to a hallucination, a mirage is a real optical phenomenon that can be captured on camera, since light rays are actually refracted to form the false image at the observer's location.
Superior mirage series#
Mirages can be categorized as "inferior" (meaning lower), "superior" (meaning higher) and " Fata Morgana", one kind of superior mirage consisting of a series of unusually elaborate, vertically stacked images, which form one rapidly-changing mirage. The word comes to English via the French (se) mirer, from the Latin mirari, meaning "to look at, to wonder at". Ī mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. Various kinds of mirages in one location taken over the course of six minutes, not shown in chronological order.
0 kommentar(er)
