Kepler's laws of planetary motion

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kepler-first-law

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kepler-second-law

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Johannes Kepler
Johannes Kepler, the formulator of the laws
Born	27 December 1571 Weil der Stadt, Holy Roman Empire
Died	15 November 1630 Regensburg, Holy Roman Empire
Nationality	German
Known for	Kepler's laws of planetary motion
Scientific career
Fields	Astronomy, Mathematics, Astrology

Kepler's laws of planetary motion are three scientific laws describing the motion of planets around the Sun. Formulated by the German astronomer Johannes Kepler between 1609 and 1619, these laws improved upon the earlier geocentric model and heliocentric models of the Solar System.

First Law: The Law of Ellipses

Main article: Kepler's First Law

Kepler's First Law states that the orbit of a planet is an ellipse with the Sun at one of the two foci. This law challenged the long-held belief that planetary orbits were perfect circles, as proposed by Claudius Ptolemy and later by Nicolaus Copernicus.

Second Law: The Law of Equal Areas

Main article: Kepler's Second Law

Kepler's Second Law, also known as the Law of Equal Areas, states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. This implies that a planet moves faster when it is closer to the Sun and slower when it is farther from the Sun. This law is a consequence of the conservation of angular momentum.

Third Law: The Law of Harmonies

Main article: Kepler's Third Law

Kepler's Third Law, or the Law of Harmonies, states that the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit. Mathematically, it can be expressed as: \[ T^2 \propto a^3 \] where \( T \) is the orbital period and \( a \) is the semi-major axis. This law provided a relationship between the distance of planets from the Sun and their orbital periods, further supporting the heliocentric model.

Historical Context

Kepler's laws were derived from the meticulous observations of Tycho Brahe, whose data on planetary positions were the most accurate available at the time. Kepler's work laid the foundation for Isaac Newton's theory of universal gravitation, which provided a physical explanation for the laws.

Applications

Kepler's laws are fundamental in the field of celestial mechanics and are used to predict the positions of planets, comets, and other celestial bodies. They are also essential in the planning of space missions and the study of exoplanets.

Related Pages

• Johannes Kepler
• Tycho Brahe
• Isaac Newton
• Heliocentric model
• Geocentric model
• Orbital mechanics
• Elliptic orbit
• Angular momentum
• Universal gravitation

See Also

• Newton's laws of motion
• Orbital period
• Semi-major axis
• Astronomy
• Astrophysics