Question

How do we know Hubble's Constant?

Answer 1

`"time"="displacement"/"velocity"`

`"velocity"/"displacement"=1/"time"`

If you were to plot a graph of the distances between Earth and other galaxies and celestial objects beyond our galaxy against their recessional velocity, you'll get an approximate straight line through the constant.

`v=H_0d`

`v_0/d_0=H_0`

The change in recessional velocity over the change in distance is given as the Hubble constant. This is why it is sometimes given as `km` `s^-1 Mpc^-1`, it is `(Deltav)/(Deltad)=(kmcolor(white)(l)s^-1)/(Mpc)`. Mpc is used to simplify the great distances between galaxies.