The sun, mass 2.0 X 10^30 kg, is revolving regarding the center of the Milky Way galaxy, which is 2.2 X 10^20 m away. It completes one revolution each 2.5 X 10^8 years. Estimate the number of stars in the Milky Way.
(Hint: Suppose for simplicity that the stars are distributed with spherical symmetry about the galactic center and that our sun is basically at the galactic edge)