Assume our Sun orbits the Milky Way galaxy at a constant radius of r = 2.6 x 1020m from the galactic center. If the period of rotation is 200 My (1 My = 1 million years), what is the Milky Way galaxy's mass, M? Assuming that the galaxy is made of stars and that the average mass of a star is equal to the mass of the Sun, approximately how many stars are there in the Milky Way? Assume (incorrectly) that the galaxy is essentially spherical and that most if its mass lies interior to the Sun's orbit.

Assume our Sun orbits the Milky Way galaxy at a constant radius of r = 2.6 x 1020m from the galactic center. If the period of rotation is 200 My (1 My = 1 million years), what is the Milky Way galaxy's mass, M? Assuming that the galaxy is made of stars and that the average mass of a star is equal to the mass of the Sun, approximately how many stars are there in the Milky Way? Assume (incorrectly) that the galaxy is essentially spherical and that most if its mass lies interior to the Sun's orbit.