Find the major axis of the orbit using the small - angle formula Size = angular size distance Size of the orbit METERS Find the size of the semimajor axis by dividing the major axis by 2 meters Finally , recalling the gravitational constant G = 6.67 * 10 " mike's ( meters cubed per kilogram seconds squared ) find the mass of the object at the center of the galaxy usin Newton's form of Kepler's third law : AT 471 9 Q P Mass of object at center of galaxy Not