question: Why does a mirage reflect the ground and area in front of it? E.G a car traveling on the highway where you can see the reflection on the road.
comment: It is a complicated concept which uses refraction, critical angles, snells law, etc. First you need to understand refraction. This happens when lights moves from one medium to another. Say water to air. This you can notice in a pool, where if you put a stick half way in water and half outside, you will see it bend. This bending of light is called refraction. This is caused due to differing densities of the two mediums. When light travels from a medium of higher to lower density. It bends away from the vertical. When it goes from lower to higher density it bends towards the vertical. This is explained in more detail using snells law. We are interested in the first case where light bends away. The angle at which it bends( angle of refraction) is proportional to the angle at which the light is hitting the transition surface (agngle of incidence) between the two mediums. Now as that angle of incidence keeps increases the angle of refraction keeps increasing as well. Now since the light bends away from the vertical in this case the angle of refraction will always be greater than the angle of incidence. As the angle of incidence gets close to the horizontal (or the horizon where you usually see a mirage) this angle becomes so big that the angle of refraction is now parallel to the ground. So the angle of refraction now starts to just come back into the same medium where it started. Hope that makes sense. So a mirage is just that but inverted, where the hotter air closer to the ground has lesser density than the cooler air above it. So when light comes from the cooler(more denser) air to the hotter (less denser) air it starts to refract. As you watch the objects closer to the horizon, the angle of incidence increase which proportionally increases the angle of refraction, and when you reach the critical angle, it just starts reflecting back (like a mirror).
passages: Fata Morgana mirages are most common in polar regions, especially over large sheets of ice with a uniform low temperature, but they can be observed almost anywhere. In polar regions, a Fata Morgana may be observed on cold days; in desert areas and over oceans and lakes, a Fata Morgana may be observed on hot days. For a Fata Morgana, temperature inversion has to be strong enough that light rays' curvatures within the inversion are stronger than the curvature of the Earth.
   In the first fourteen frames, elements of the Fata Morgana mirage display alternations of compressed and stretched zones. The last two frames were photographed a few hours later, around sunset time. At that point in time, the air was cooler while the ocean was probably a little bit warmer, which caused the thermal inversion to be not as extreme as it was few hours before. A mirage was still present at that point, but it was not so complex as a few hours before sunset: the mirage was no longer a Fata Morgana, but instead had become a simple superior mirage.
   The rays will bend and create arcs. An observer needs to be within an atmospheric duct to be able to see a Fata Morgana.
  
  Fata Morgana mirages may be observed from any altitude within the Earth's atmosphere, including from mountaintops or airplanes. 
   Section::::Night-time mirages.
  
  The conditions for producing a mirage can take place at night. Under most conditions, these are not observed. However, under some circumstances lights from moving vehicles, aircraft, ships, buildings, etc. can be observed at night, even though, as with a daytime mirage, they would not be observable.
  
  This includes the mirage of astronomical objects.
  
  Section::::Night-time mirages.:Mirage of astronomical objects.
   Section::::Famous legends and observations.:Phantom islands.:Croker Mountains.
   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.
   A Fata Morgana, the name of which comes from the Italian translation of Morgan le Fay, the fairy shapeshifting half-sister of King Arthur, is a very complex superior mirage. It appears with alternations of compressed and stretched areas, erect images, and inverted images. A Fata Morgana is also a fast-changing mirage.
   The optical phenomenon occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed. (A thermal inversion is an atmospheric condition where warmer air exists in a well-defined layer above a layer of significantly cooler air. This temperature inversion is the opposite of what is normally the case; air is usually warmer close to the surface, and cooler higher up.)
   Fata Morgana mirages tremendously distort the object or objects which they are based on, such that the object often appears to be very unusual, and may even be transformed in such a way that it is completely unrecognizable. A Fata Morgana can be seen on land or at sea, in polar regions or in deserts. This kind of mirage can involve almost any kind of distant object, including such things as boats, islands, and coastline.
   A Fata Morgana may be described as a very complex superior mirage with more than three distorted erect and inverted images. Because of the constantly changing conditions of the atmosphere, a Fata Morgana may change in various ways within just a few seconds of time, including changing to become a straightforward superior mirage.
  
  The sequential image here shows sixteen photographic frames of a mirage of the Farallon Islands as seen from San Francisco; the images were all taken on the same day.
   Mirage (DC Comics)
  
  Mirage is the name of two DC Comics characters. The first was a minor villain of Batman. The second is a heroine who is affiliated with the Teen Titans.
  
  Section::::Batman foe.
   If the vertical temperature gradient is +12.9 °C per 100 meters (where the positive sign means temperature gets hotter as one goes higher) then horizontal light rays will just follow the curvature of the Earth, and the horizon will appear flat. If the gradient is less (as it almost always is) the rays are not bent enough and get lost in space, which is the normal situation of a spherical, convex "horizon".
  
  In some situations, distant objects can get elevated or lowered, stretched or shortened with no mirage involved.
  
  Section::::Superior mirage.:Fata Morgana.
   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.
   Superior mirages are quite common in polar regions, especially over large sheets of ice that have a uniform low temperature. Superior mirages also occur at more moderate latitudes, although in those cases they are weaker and tend to be less smooth and stable. For example, a distant shoreline may appear to "tower" and look higher (and, thus, perhaps closer) than it really is. Because of the turbulence, there appear to be dancing spikes and towers. This type of mirage is also called the Fata Morgana or "hafgerdingar" in the Icelandic language.
   A superior mirage occurs when the air below the line of sight is colder than the air above it. This unusual arrangement is called a temperature inversion, since warm air above cold air is the opposite of the normal temperature gradient of the atmosphere. Passing through the temperature inversion, the light rays are bent down, and so the image appears above the true object, hence the name "superior". Superior mirages are in general less common than inferior mirages, but, when they do occur, they tend to be more stable, as cold air has no tendency to move up and warm air has no tendency to move down.
   Mirage
  
  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.
   Fata Morgana mirages are visible to the naked eye, but in order to be able to see the detail within them, it is best to view them through binoculars, a telescope, or as is the case in the images here, through a telephoto lens.
  
  Gabriel Gruber (1740–1805) and (1744–1806), who observed Fata Morgana above Lake Cerknica, were the first to study it in a laboratory setting.
  
  Section::::Etymology.
   Section::::Development.
   A Fata Morgana is most commonly seen in polar regions, especially over large sheets of ice that have a uniform low temperature. It may, however, be observed in almost any area. In polar regions the Fata Morgana phenomenon is observed on relatively cold days. In deserts, over oceans, and over lakes, however, a Fata Morgana may be observed on hot days.
   Looming and similar refraction phenomena
  
  While mirages are the best known atmospheric refraction phenomena, looming and similar refraction phenomena do not produce mirages. Mirages show an extra image or images of the miraged object, while looming, towering, stooping, and sinking do not. No inverted image is present in those phenomena either. Depending on atmospheric conditions, the objects can appear to be elevated or lowered, stretched or stooped. These phenomena can occur together, changing the appearance of different parts of the objects in different ways. Sometimes these phenomena can occur together with a true mirage.
  
  Section::::Looming.
   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 watersurface.
  
  Section::::Inferior mirage.
   In the lines, "the weary traveller sees / In desert or prairie vast, / Blue lakes, overhung with trees / That a pleasant shadow cast", because of the mention of blue lakes, it is clear that the author is actually describing not a Fata Morgana, but rather a common inferior or desert mirage. The 1886 drawing shown here of a "Fata Morgana" in a desert might have been an imaginative illustration for the poem, but in reality no mirage ever looks like this. Andy Young writes, "They're always confined to a narrow strip of sky—less than a finger's width at arm's length—at the horizon."
   Superior mirages can have a striking effect due to the Earth's curvature. Were the Earth flat, light rays that bend down would soon hit the ground and only nearby objects would be affected. Since Earth is round, if their downward bending curve is about the same as the curvature of the Earth, light rays can travel large distances, perhaps from beyond the horizon. This was observed and documented for the first time in 1596, when a ship under the command of Willem Barentsz in search of the Northeast passage became stuck in the ice at Novaya Zemlya. The crew was forced to endure the polar winter there. They saw their midwinter night come to an end with the rise of a distorted Sun about two weeks earlier than expected. It was not until the 20th century that science could explain the reason: the real Sun had still been below the horizon, but its light rays followed the curvature of the Earth. This effect is often called a Novaya Zemlya mirage. For every the light rays can travel parallel to the Earth's surface, the Sun will appear 1° higher on the horizon. The inversion layer must have just the right temperature gradient over the whole distance to make this possible.
   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.
   To generate the Fata Morgana phenomenon, the thermal inversion has to be strong enough that the curvature of the light rays within the inversion layer is stronger than the curvature of the Earth. Under these conditions, the rays bend and create arcs. An observer needs to be within or below an atmospheric duct in order to be able to see a Fata Morgana.
  
  A Fata Morgana may be observed from any altitude within the Earth's atmosphere, from sea level up to mountaintops, and even including the view from airplanes.
  