Editing Refraction (section)

==On water==
[[File:Pencil in a bowl of water.svg|left|thumb|A pencil part immersed in water looks bent due to refraction: the light waves from X change direction and so seem to originate at Y.]]

Refraction occurs when light goes through a water surface since water has a refractive index of 1.33 and air has a refractive index of about 1. Looking at a straight object, such as a pencil in the figure here, which is placed at a slant, partially in the water, the object appears to bend at the water's surface. This is due to the bending of light rays as they move from the water to the air. Once the rays reach the eye, the eye traces them back as straight lines (lines of sight). The lines of sight (shown as dashed lines) intersect at a higher position than where the actual rays originated. This causes the pencil to appear higher and the water to appear shallower than it really is.

The depth that the water appears to be when viewed from above is known as the ''apparent depth''. This is an important consideration for [[spearfishing]] from the surface because it will make the target fish appear to be in a different place, and the fisher must aim lower to catch the fish. Conversely, an object above the water has a higher ''apparent height'' when viewed from below the water. The opposite correction must be made by an [[archer fish]].<ref>{{cite journal|doi=10.1007/BF00361900|journal=Behavioral Ecology and Sociobiology|volume=2 |year=1977|issue =2|pages=169–184|title=Refraction and the spitting behavior of the archerfish (''Toxotes chatareus'')|author=Dill, Lawrence M. |jstor=4599128|bibcode=1977BEcoS...2..169D |s2cid=14111919}}</ref>

For small angles of incidence (measured from the normal, when {{math|sin ''θ''}} is approximately the same as {{math|tan ''θ''}}), the ratio of apparent to real depth is the ratio of the refractive indexes of air to that of water. But, as the angle of incidence approaches 90°, the apparent depth approaches zero, albeit reflection increases, which limits observation at high angles of incidence. Conversely, the apparent height approaches infinity as the angle of incidence (from below) increases, but even earlier, as the angle of [[total internal reflection]] is approached, albeit the image also fades from view as this limit is approached.

[[File:GGB reflection in raindrops.jpg|thumb|An image of the [[Golden Gate Bridge]] is refracted and bent by many differing three-dimensional drops of water.]]