| radial velocity |
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The velocity of an object relative to an observer as measured in the direction of the line of sight. To determine an object's true velocity in space, it is necessary also to know the transverse velocity, which is across the line of sight. For stars, galaxies and other astronomical objects, the radial velocity is often much easier to determine than the transverse velocity because of the operation of the Doppler effect. See also: proper motion. |