What is the Hubble constant essentially a measure of?

Jun 26, 2016

Recession (expansion) speed of the space in-between two galaxies.
As of now, the Hubble constant is nearly 71 km/sec/mega parsec.

Explanation:

A quasar is what appears as a point source of light, in a far distant

galaxy. Perhaps, it is the Black Hole of the galaxy. Measurements

reveal that this source is receding from the Earth (of the

galaxy Milky Way). This is how Hubble constant is estimated. A

generalization,based on recession of different quasars from Milky

Way, leads to the notion of expansion of our universe.