The Hubble Constant: measures distance using parallax angles measures the difference between absolute and apparent magnitude is a relationship between distance and velocity can only be used to measure distances of close stars

Answer;

is a relationship between distance and velocity

Explanation; According to Hubble's Law the recessional speed of a galaxy is directly proportional to its distance. The Hubble Constant is the unit of measurement used to describe the expansion of the universe, it is the relationship of the recessional speed of a galaxy and its distance. The formula showing the relationship is given by the formula:

v = Hd, where: v = velocity of a galaxy, in km/s. H = Hubble Constant, measured in km/s/Mpc and d is the distance in km.