The sun is considered to be a satellite of our galaxy, the Milky Way. The sun revolves around the center of the galaxy with a radius of 2.2 x 1020 m. The period of one revolution is 2.5 x 108 years.
1. Discover the mass of the galaxy.
2. Discover the speed with which the sun moves around the center of the galaxy.
3. Assuming that the average star in the galaxy has the same mass as the sun, find the number of stars.