This corrects for both apparent dip and terrestrial refraction.
2.
"' Terrestrial refraction "', sometimes called "'geodetic refraction "', deals with the apparent angular position and measured distance of terrestrial bodies.
3.
As a common approximation, terrestrial refraction is considered as a constant bending of the ray of light or line of sight, in which the ray can be considered as describing a circular path.
4.
Terrestrial refraction usually causes terrestrial objects to appear higher than they really are, although in the afternoon when the air near the ground is heated, the rays can curve upward making objects appear lower than they really are.
5.
Since the line of sight in terrestrial refraction passes near the earth's surface, the magnitude of refraction depends chiefly on the temperature gradient near the ground, which varies widely at different times of day, seasons of the year, the nature of the terrain, the state of the weather, and other factors.
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