Question

What is the explanation behind Hubble's constant?

Answer 1

It is the rate of the universe expansion.

Explanation:

Hubble's Law `("velocity of expansion" = H_0*"distance")`

... is interpreted with the constant (which is arguably a constant because it shows variations through time). This important law also supports Doppler effect, which, in turn, agrees with the cosmic expansion of the universe.

I understand Hubble's constant`(H_0~~60-85 "km"/s)` as the velocity (rate) at which galaxies are driving away from each other as the universe expands metrically in all directions.