State Kepler's law of planetary motion.

Explanation

Kepler's law (Law of orbit) : All planets revolve in elliptical orbits with Sun as one of its foci.
2a - Major axis length
2b - Minor axis length
S - Sun at one focus
S' - The other focus of the ellipse
P - Perihelion position of the planet .
A- Apehelion position of the planet.

Kepler's II law (Law of areas) : The line joining the planet and the Sun sweeps out equal areas in equal intervals of time.
`(Deltavec(A))/(Deltat)=1/(2m)vec(L)`

For a conservative force `|vec(L)|` is constant and hence `|(Deltavec(A))/(Deltat)|` is also a constant.
Kepler's III law (Law of periods ) : The square of the period of revolution of a planet around the sun is directly proportional to the cube of the semi major axis of the ellipse.
i.e., `T^(2) prop a^(3)` so that two planets.
`((T_(1))/(T_(1)))=(a_(1)/(a_(2)))^(3)`