Kepler's 3 Laws of planetary motion.

• The planets move in ellipse with the Sun at one focus.
• The radius vector (the line joining the centre of the Sun with the centre of the planet) sweeps out equal areas in equal times i.e. the closer to the sun the faster the planet moves and vice-versa.
• The square of the siderial period is proportional to the cube of the planet's mean distance from the Sun.

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