Since the Hubble constant H 0 can be found by dividing velocity by distance,
it is customarily written in the rather baroque units of km s −1 Mpc −1
. When
Hubble first discovered Hubble’s Law, he thought that the numerical value of
the Hubble constant was H 0 = 500 km s −1 Mpc −1
(see Figure 2.4). However,
it turned out that Hubble was severely underestimating the distances to
galaxies.