For 10 points, name this constant that relates recessional velocity, or redshift, to distance.
The density parameter, omega, is inversely proportional to three times this quantity squared. This quantity is constant for a comoving time and is equal to the time derivative of the scale factor divided by the scale factor. Because this quantity has units of 1 over time, its inverse gives the predicted (*) age of the universe. It was originally calculated from its namesake's study of Cepheid variables, and current values for it range between 65 to 75 kilometers per second per megaparsec. For 10 points, name this constant that relates recessional velocity, or redshift, to distance.
The density parameter, omega, is inversely proportional to three times this quantity squared.
Hubble's constant [or Hubble parameter; or anything mentioning Edwin Hubble]