Astronomers measure distances to faraway galaxies and their velocities .
They do that in order to determine the expansion rate of the Universe .
In Part I of these lectures the foundations of the theory of the expansion of the Universe was given .
In this part we present the theory .
A formula for the distance of the galaxy in terms of its velocity is given .
It is very simple : r ( v ) = c \tau / \beta \sinh \beta v / c , where \tau is the Big Bang time , \beta = \sqrt { 1 - \Omega _ { m } } , and \Omega _ { m } is the mass density of the Universe .
For \Omega _ { m } < 1 this formula clearly indicates that the Universe is expanding with acceleration , as experiments clearly show .