How many stars are in the Milky Way?

As is typical for many galaxies, the distribution of mass in the Milky Way is such that the orbital speed of most stars in the galaxy does not depend strongly on its distance from the center. Away from the central bulge or outer rim, the typical stellar velocity is between 210 and 240 km/s. Hence the orbital period of the typical star is directly proportional only to the length of the path travelled. This is unlike in the solar system where different orbits are also expected to have significantly different velocities associated with them, and is one of the major pieces of evidence for the existence of dark matter.