Mirage

Various kinds of mirages in one location taken over the course of six minutes, not shown in temporal order. The uppermost inset frame shows an inferior mirage of the Farallon Islands. The second inset frame is the Farallon Islands with a green flash on the left-hand side. The two lower frames and the main frame all show superior mirages of the Farallon Islands. In these three frames, the superior mirages evolve from a 3-image mirage (an inverted image between two erect ones) to a 5-image mirage, and then back to a 2-image mirage. Such a display is consistent with a Fata Morgana. All frames but the upper one were photographed from about 50–70 feet above sea level. The upper frame was photographed from sea level.

A mirage is a naturally occurring optical phenomenon in which light rays bend to produce a displaced image of distant objects or the sky. The word comes to English via the French mirage, from the Latin mirari, meaning "to look at, to wonder at". This is the same root as for "mirror" and "to admire".

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.

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. What the image appears to represent, however, is determined by the interpretive faculties of the human mind. For example, inferior images on land are very easily mistaken for the reflections from a small body of water.

Inferior mirage

An inferior mirage on the Mojave Desert in spring

For exhausted travelers in the desert, an inferior mirage may appear to be a lake of water in the distance. An inferior mirage is called "inferior" because the mirage is located under the real object. The real object in an inferior mirage is the (blue) sky or any distant (therefore bluish) object in that same direction. The mirage causes the observer to see a bright and bluish patch on the ground in the distance which is also called oasis mirage.

Light rays coming from a particular distant object all travel through nearly the same air layers and all are bent over about the same amount. Therefore, rays coming from the top of the object will arrive lower than those from the bottom. The image usually is upside down, enhancing the illusion that the sky image seen in the distance is really a water or oil puddle acting as a mirror.

Inferior images are not stable. Hot air rises, and cooler air (being more dense) descends, so the layers will mix, giving rise to turbulence. The image will be distorted accordingly. It may be vibrating; it may be vertically extended (towering) or horizontally extended (stooping). If there are several temperature layers, several mirages may mix, perhaps causing double images. In any case, mirages are usually not larger than about half a degree high (same apparent size as the sun and moon) and from objects only a few kilometers away.

Heat haze

Heat haze caused by jet engine exhaust

Heat haze, also called heat shimmer, refers to the inferior mirage experienced when viewing objects through a layer of heated air; for example, viewing objects across hot asphalt or through the exhaust gases produced by jet engines. When appearing on roads due to the hot asphalt, it is often referred to as a highway mirage.

Convection 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 creates a gradient in the refractive index of the air. This produces a blurred shimmering effect, which affects the ability to resolve objects, the effect being increased when the image is magnified through a telescope or telephoto lens.

A hot-road mirage, "fake water" on the road, the most common example of an inferior mirage

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. The mind interprets this as a pool of water on the road, since water also reflects the sky. The illusion fades as one gets closer.

On tarmac roads it may look as if water, or even oil, has been spilled. These kinds of inferior mirages are often called "desert mirages" or "highway mirages". Both sand and tarmac can become very hot when exposed to the sun, easily being more than 10 °C hotter than the air one meter above, enough to create conditions suitable for the formation of the mirage.

Heat haze is not related to the atmospheric phenomenon of haze.

Other Languages
العربية: سراب
ܐܪܡܝܐ: ܗܪܗܪܐ
অসমীয়া: মৰীচিকা
asturianu: Espeyismu
azərbaycanca: İlğım
تۆرکجه: ایلغیم
বাংলা: মরীচিকা
беларуская: Міраж
беларуская (тарашкевіца)‎: Міраж
български: Мираж
català: Miratge
Чӑвашла: Мираж
chiShona: Musami
eesti: Miraaž
español: Espejismo
فارسی: سراب
français: Mirage
Gaeilge: Meabhalscáil
한국어: 신기루
հայերեն: Միրաժ
हिन्दी: मरीचिका
hrvatski: Miraž
Ido: Mirajo
interlingua: Mirage
íslenska: Hillingar
italiano: Miraggio
ქართული: მირაჟი
қазақша: Сағым
Kreyòl ayisyen: Mirage
Кыргызча: Мираж
latviešu: Mirāža
lietuvių: Miražas
മലയാളം: മരീചിക
मराठी: मृगजळ
Bahasa Melayu: Logamaya
日本語: 蜃気楼
norsk nynorsk: Luftspegling
occitan: Miratge
polski: Miraż
português: Miragem
русский: Мираж
shqip: Mirazhi
Simple English: Mirage
کوردی: تراویلکە
srpskohrvatski / српскохрватски: Miraž
suomi: Kangastus
svenska: Hägring
татарча/tatarça: Рәшә
తెలుగు: ఎండమావి
ไทย: มิราจ
Türkçe: Serap
українська: Міраж
Tiếng Việt: Ảo tượng
粵語: 海市蜃樓
中文: 海市蜃楼