An Etymological Dictionary of Astronomy and Astrophysics
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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.

→ acceleration; → parameter.