Figure 2: Illustration of the Hubble law. Galaxies at all points of the square grid are receding from
the black galaxy at the centre, with velocities proportional to their distance away from it. From the
point of view of the second, green, galaxy two grid points to the left, all velocities are modified by
vector addition of its velocity relative to the black galaxy (red arrows). When this is done, velocities
of galaxies as seen by the second galaxy are indicated by green arrows; they all appear to recede
from this galaxy, again with a Hubble-law linear dependence of velocity on distance.