Velocity dispersion

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In astronomy, the

By measuring the radial velocities of selected members, the velocity dispersion of the cluster can be estimated and used to derive the cluster's mass from the virial theorem.

**velocity dispersion**σ, is the range of velocities about the mean velocity for a group of objects, such as a cluster of stars about a galaxy. For example, in a galaxy, a typical value for the velocity dispersion of the objects orbiting the galactic centre is about 200km/s.By measuring the radial velocities of selected members, the velocity dispersion of the cluster can be estimated and used to derive the cluster's mass from the virial theorem.