A German astronomer, Johann Kepler, first stated the laws of planetary motion.

**The three laws of planetary motion are:**

**The law of orbits:**Every planet moves in an elliptical orbit having the sun at one of the foci.**The law of areas:**The line joining any planet to the sun sweeps out equal areas in equal intervals of time. That is, the areal velocity of the planet is constant.**The law of periods:**The square of the time period of revolution of a planet around the sun is proportional to the cube of the planet’s mean distance from the sun.

**Explanation**

**1 ^{st} law: **ABCD is an elliptical orbit. F and F’ are the two foci. According to the 1

^{st}law, the orbit of the planet is elliptical with the sun, as it’s one of the foci.

**2 ^{nd} law: **Let the sun is at the focus F. If a planet takes time t coming from A to B, then it will take the same time to come from C to D.

Therefore, according to 2^{nd} law,

Area of AFB = area of CFD

**3 ^{rd} law:** Since the planets orbiting the sun in an elliptical orbit, so the distance of a planet will be different for different time.

Let the average distance of a planet from the sun = R and the planet take T time to round the sun once.

According to the 3^{rd} Law, T ∝ R^{3}