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# Kepler's Law of Gravitation

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#### Kepler's Law of Gravitation - Lesson Summary

Keplerâ€™s Laws of Planetary Motion
The universe is one of the most fascinating subjects that were explored by many people around the world. Johannes Kepler, a student of Tyco Brahe, suggested three laws about the motion of the planets in the solar system, which revolutionised the comprehension about our solar system. These laws are named after him as Keplerâ€™s laws of planetary motion.

According to Keplerâ€™s theory, all the planets revolve around the sun in elongated orbits, rather than perfect circles.

Keplerâ€™s three laws of planetary motion are:
â€¢  The law of orbits
â€¢  The law of areas and
â€¢  The law of periods

Keplerâ€™s first law
Keplerâ€™s first law, the law of orbits, states that the orbit of a planet is an ellipse with the sun at one of the foci. An ellipse is a closed, curved shape that is defined by two points called foci representing an elongated circle.The closest point on a planetâ€™s orbit from the sun is called perihelion and the farthest point from the sun is called the aphelion.

Keplerâ€™s second law
Keplerâ€™s second law of planetary motion, also known as the law of areas, states that the line joining the planet to the sun sweeps out equal areas in equal intervals of time as the planet travels in its orbit.

Keplerâ€™s third law
Keplerâ€™s third law, the law of periods, defines the relationship between the orbital period of a planet and the average radius of its orbit. The orbital period of a planet, denoted by T, is the time taken by the planet to make a complete revolution around the sun along its orbit.

The average radius of the orbit of a planet is also the mean distance of the planet from the sun.

The law of periods states that the square of orbital period, T, of a planet is proportional to the cube of its mean distance, R, from the sun.

The law of periods can be expressed as T 2 Î± R 3.