Final answer:
The mass of the Milky Way has been determined by measuring the velocity of objects in its outer regions and applying Kepler's Third Law, resulting in an estimate of 100 billion solar masses.
Step-by-step explanation:
The mass of our galaxy, the Milky Way, has been calculated using a technique that involves measuring the velocities of objects orbiting the galactic center and then applying Kepler's Third Law. This law allows us to use the orbiting speed to estimate the mass within a given orbit. We assume the Sun's orbit is circular and that the mass within the Sun's orbit can be treated as if it were concentrated at the galaxy's center. This has led to the discovery that the Milky Way has a mass of about 100 billion times that of the Sun. Such calculations initially presumed that there would be minimal mass beyond the Sun's orbit, but newer models acknowledge more mass further out, largely due to dark matter.