Question

A. The Sun travels in a circular orbit at a velocity of 220 km/second at a distance of 8.0 kiloparsecs from the center of the Galaxy (note that these numbers are slightly different from those in your book). Calculate the number of years it takes the Sun to complete an orbit (i.e., the circumference of a circle with an 8.0 kiloparsec radius) around the center of the Galaxy. (There are 3.1 x 1013 kilometers/parsec and 3.2 x 107 seconds/year.)

B. . One can make a more general version of Kepler's Third Law which accounts for the mass of the object being orbited M P2 = a3 Everything works if P is expressed in years, a is expressed in astronomical units (AU), and M is in units of the Sun's mass (so in our solar system, M=1). You can apply this equation to an entire galaxy of stars, in which case you measure the mass which lies interior to the orbit of the star for which you know "a" and "P". The Milky Way Galaxy is approximately 3x109AU in radius. The Sun orbits the center of the Galaxy at a distance of a=2x109AU. Using the result of the previous problem, calculate how much mass of the Milky Way is contained inside the Sun's orbit?

Answer 1