http://www.physicsclassroom.com/class/circles/Lesson-4/Mathematics-of-Satellite-Motion
T^2/R^3 = constant for any old star
A planet orbiting a certain star is observed to have an orbital period of 65 days with an orbit whose semi-major axis is 3.8 × 107 km. A second planet orbiting the same star has an orbital period of 450 d. What is the semi-major axis of its orbit?
1 answer