# How do we know Hubble's Constant?

Mar 9, 2018

$\text{time"="displacement"/"velocity}$

$\text{velocity"/"displacement"=1/"time}$

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.

$v = {H}_{0} d$

${v}_{0} / {d}_{0} = {H}_{0}$

The change in recessional velocity over the change in distance is given as the Hubble constant. This is why it is sometimes given as $k m$ ${s}^{-} 1 M p {c}^{-} 1$, it is $\frac{\Delta v}{\Delta d} = \frac{k m \textcolor{w h i t e}{l} {s}^{-} 1}{M p c}$. Mpc is used to simplify the great distances between galaxies.