What two observations allow us to estimate the Galaxy's mass?
a) the Sun's mass and velocity in orbit around the galactic center
b) the rotation of the bulge and disk components
c) the Sun's age and age of the globular cluster stars
d) the motion of spiral arms and the mass of the central black hole
e) the orbital period and distance from the galactic center of objects near the edge of the Galaxy
Answer: e) the orbital period and distance from the galactic center of objects near the edge of the Galaxy