Recessional velocity

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Recessional Velocity is a term used to describe the rate at which an object is moving away, typically from Earth.

[edit] Application to Cosmology

This term is generally only used in reference to distant Galaxies. The most common reason for the use of this term is Hubble's Law, which states that the Recessional Velocity is proportional to the distance between an inertial observer and a distant galaxy. According to the equation

v = H₀D

where H₀ is the Hubble constant, D is the intervening distance, and v is the Recessional Velocity, generally measured in km/s.

The Recessional Velocity is usually measured from the redshift observed in the electromagnetic radiation emitted by the galaxy and then the distance to that galaxy is estimated, using Hubble's Law.