<P> Objects that are gravitationally bound will rotate around a common center of mass . For stellar bodies, this motion is known as peculiar velocity, and can alter the Hubble Flow . Thus, an extra term for the peculiar motion needs to be added to Hubble's law: </P> <Dl> <Dd> v t o t a l = H 0 d + v p e c (\ displaystyle v_ (total) = H_ (0) d + v_ (pec)) </Dd> </Dl> <Dd> v t o t a l = H 0 d + v p e c (\ displaystyle v_ (total) = H_ (0) d + v_ (pec)) </Dd> <P> This motion can cause confusion when looking at a solar or galactic spectrum, because the expected redshift based on the simple Hubble law will be obscured by the peculiar motion . For example, the shape and size of the Virgo Cluster has been a matter of great scientific scrutiny due to the very large peculiar velocities of the galaxies in the cluster . </P>

Which of the following cannot be measured from the optical absorption spectrum of the sun