An Etymological Dictionary of Astronomy and Astrophysics

A measure of the departure from a constant rate of the acceleration of the Universe, expressed by:
q(t) = R(t)R ^..(t)/R ^.2(t), where R(t) represents the size of the Universe at time t. Traditionally, a negative sign is inserted in the above equation for the → deceleration parameter.

See also: → acceleration; → parameter.