the deflection or deviation of a wave, e.g. a beam of light, from one straight path to another when passing at an angle from one medium into another, e.g. from glass into air
the deflection or deviation of a wave, e.g. a beam of light, from one straight path to another when passing from one medium, e.g. air, into another, e.g. glass, in which the speed of transmission of the wave is different
the amount of deviation of a wave undergoing refraction
the change in the apparent position of a celestial body due to bending of the light rays coming from it as they pass through the atmosphere
the correction to be applied to the apparent position of a body because of this