## Dimensionless Hubble parameter

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Dimensionless Hubble parameter$h$ is related to the Hubble constant$H_0$ via
This definition is used almost unanimously in modern cosmology and astrophysics. Previous (now almost obsolete) notations include $h_{50} = H_0/50\;{\rm km/sec/Mpc}$ or $h_{70} = H_0/70\;{\rm km/sec/Mpc}$