# what is kepler’s 3rd law Kepler’s Third Law. Kepler discovered that the size of a planet’s orbit (the semi-major axis of the ellipse) is simply related to sidereal period of the orbit. If the size of the orbit (a) is expressed in astronomical units (1 AU equals the average distance between the Earth and the Sun) and the period (P) is measured in years, …

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• ### Why is Kepler’s 3rd law important?

• Kepler’s 3rd law is a mathematical formula. It means that if you know the period of a planet’s orbit (P = how long it takes the planet to go around the Sun), then you can determine that planet’s distance from the Sun (a = the semimajor axis of the planet’s orbit). Why is Kepler’s first law important?

• ### What are the 3 laws of planetary motion?

• In astronomy, Kepler鈥檚 laws of planetary motion are three scientific laws describing the motion of planets around the sun. Kepler first law 鈥?The law of orbits. Kepler鈥檚 second law 鈥?The law of equal areas. Kepler鈥檚 third law 鈥?The law of periods.

• ### What is the value of K in the Keplerian model?

• The value k is related to physical constants such that k = 4pi 2 /GM where G is the gravitational constant and M the mass of the object at the centre of the orbit (NOT the object doing the orbiting!) How did Kepler arrive at this result?

• ### Did Kepler believe in the heliocentric model of the Solar System?

• As it turned out, Kepler, unlike Brahe, believed firmly in the Copernican model of the solar system known as heliocentric, which correctly placed the Sun at its center. But the reason Mars’ orbit was problematic was because the Copernican system incorrectly assumed the orbits of the planets to be circular.