Question

Explain why Kepler’s third law applies to the orbits of comets but not to the orbits of satellites.

Answer 1

Kepler’s laws apply to objects that revolve around the Sun. Its complete form is: 

p² = k a³ 

where k is a proportionality constant. 

When this relation is applied to the Earth for which p = 1.0 y and a = 1.0 AU, k = 1.0 . 

Therefore, Kepler’s third law takes the form:

p² = a³ but p must be expressed in years and a must be in AU and the object must revolve around the Sun rather than around a planet.