Editing Refraction (section)

==Atmospheric==
{{Main|Atmospheric refraction}}
[[File:mirage_principle.svg|thumb|left|Comparison of inferior and superior mirages due to differing air refractive indices, ''n'']]
[[File:Blackbird-sunset-03.jpg|thumb|The sun appears slightly flattened when close to the horizon due to refraction in the atmosphere.]]
The refractive index of air depends on the air [[density]] and thus vary with air [[temperature]] and [[pressure]]. Since the pressure is lower at higher altitudes, the refractive index is also lower, causing light rays to refract towards the earth surface when traveling long distances through the atmosphere. This shifts the apparent positions of stars slightly when they are close to the horizon and makes the sun visible before it geometrically rises above the horizon during a sunrise.

[[File:66599 , Tupton.jpg|thumb|left|[[Heat haze]] in the engine exhaust above a diesel [[locomotive]]]]
Temperature variations in the air can also cause refraction of light. This can be seen as a [[heat haze]] when hot and cold air is mixed e.g. over a fire, in engine exhaust, or when opening a window on a cold day. This makes objects viewed through the mixed air appear to shimmer or move around randomly as the hot and cold air moves. This effect is also visible from normal variations in air temperature during a sunny day when using high magnification [[telephoto lens]]es and is often limiting the image quality in these cases.
<ref>{{cite web |url=https://www.nikonimgsupport.com/eu/BV_article?articleNo=000006491&configured=1&lang=en_GB |title=The effect of heat haze on image quality |author=<!--Not stated--> |date=2016-07-10 |publisher= Nikon |access-date=2018-11-04 }}</ref> In a similar way, atmospheric [[turbulence]] gives rapidly varying [[distortion (optics)|distortions]] in the images of astronomical [[telescopes]] limiting the resolution of terrestrial telescopes not using [[adaptive optics]] or other techniques for overcoming these [[Astronomical seeing|atmospheric distortions]].

[[File:Mirage over a hot road.jpg|thumb|[[Mirage]] over a hot road]]
Air temperature variations close to the surface can give rise to other optical phenomena, such as [[mirage]]s and [[Fata Morgana (mirage)|Fata Morgana]]. Most commonly, air heated by a hot road on a sunny day deflects light approaching at a shallow angle towards a viewer. This makes the road appear reflecting, giving an illusion of water covering the road.