**Example:** Two satellites, Aaragon and Myst, revolve round their parent planet in circular orbits of radii 1000 and 400 kms respectively. What is the ratio of their time periods? **Solution:** Kepler's third law of planetary motion may be applied to satellites on noting that a circle is a special case of an ellipse. For this case, Kepler's third law may be stated as "the square of the time period is proportional to the cube of the radius of the circle." The radius of Aaragon's orbit is 1000 km and that of Myst is 400 km. Subsituting *r*_{1} = 1000 and *r*_{2} = 400, the ratio of the time periods is found to be 3.95. |