An Etymological Dictionary of Astronomy and Astrophysics

A phenomenon in which the observed and predicted phases of Venus do not coincide. At eastern elongation, when the planet is visible in the evening sky, dichotomy (half-phase) usually comes a day or two earlier than predicted, while at western elongation dichotomy occurs a day or two later.

See also: Named after Johan Schröter (1745-1816), German astronomer, who first described the effect in 1793; → effect.