Figure (11-Q2) shows the elliptical path of a planet about the sun. The two shaded parts have equal area. If t1 and t2 be the time taken by the planet to go from a to b and from c to d respectively.


From Kepler’s second law we know that a planet on a closed orbit sweeps equal areas in equal time. Hence, if the areas are equal, the time taken while traversing the arc enclosing the area will also be equal. Therefore, t1 = t2.

1