An Etymological Dictionary of Astronomy and Astrophysics

The angle between the light entering and exiting the prism when the light passing through the prism is parallel to the prism’s base. Angle of minimum deviation (D) is used to measure the → index of refraction (n) of the prism glass, because:

n = sin [(A + D)/2]/sin (A/2), where A is the → prism angle.

See also: → angle; → minimum; → deviation.