An Etymological Dictionary of Astronomy and Astrophysics

The maximum amount of the apparent yearly displacement of a star, resulting from the → aberration of starlight. The value of the constant of aberration, κ, at J2000.0 is 20".49552.

κ = (v/c) csc 1", where v is the average speed of the Earth about the Sun and c is the → speed of light in vacuum. The Earth’s speed is given by: v = 2πa / [P(1 - e²)^1/2], where a is the → semi-major axis of the Earth’s orbit, e is the → eccentricity of the Earth’s orbit, and P is the → sidereal period of the Earth. Same as → constant of annual aberration. See also → constant of diurnal aberration.

See also: → constant; → aberration.