Celestial mechanics

Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. The field applies principles of physics, historically Newtonian mechanics, to astronomical objects such as stars and planets.

History of celestial mechanics

The Ancient Greeks developed theories regarding celestial mechanics, most of which were geocentric in nature.

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Johannes Kepler

Johannes Kepler was the first to develop laws of orbits, which he did by examining and cataloging the motion of the planets. Johannes Kepler was the first to successfully model planetary orbits to a high degree of accuracy. Years before Isaac Newton had even developed his law of gravitation, Kepler had developed his three laws of planetary motion from empirical observation.

Related Topics:
Johannes Kepler - Planet - Isaac Newton

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See Kepler's laws of planetary motion and the Keplerian problem for a detailed treatment of how his laws of planetary motion can be used.

Related Topics:
Kepler's laws of planetary motion - Keplerian problem

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Isaac Newton

Isaac Newton is credited with introducing the idea that the motion of objects in the heavens, such as planets, the Sun, and the Moon, and the motion of objects on the ground, like horses and falling apples, could be described by the same set of physical laws. In this sense he unified 'celestial' and 'terrestrial' dynamics.

Related Topics:
Isaac Newton - Planets - Sun - Moon - Horses - Physical law

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Using Newton's law of gravitation, proving Kepler's Laws for the case of a circular orbit is simple. Elliptical orbits involve more complex calculations. Using Lagrangian mechanics it is possible to develop a single polar coordinate equation that can be used to describe any orbit, even those that are parabolic and hyperbolic. This is useful for calculating the behaviour of planets and comets and such. More recently, it has also become useful to calculate spacecraft trajectories.

Related Topics:
Lagrangian mechanics - Comet - Spacecraft - Trajectories

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Albert Einstein

After Einstein explained the anomalous precession of Mercury's perihelion, astronomers recognized that Newtonian mechanics did not provide the highest accuracy. Today, we have binary pulsars whose orbits not only require the use of General Relativity for their explanation, but whose evolution proves the existence of gravitational radiation, a discovery that led to a Nobel prize.

Related Topics:
Newtonian mechanics - General Relativity - Gravitational radiation

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Open problems

There are a few open problems in celestial mechanics that await solutions. The solution of the n-body problem (which is the problem of finding, given the initial positions, masses, and velocities of n bodies, their subsequent motions as determined by classical mechanics) remains unsolved. The theory of quantum mechanics has not been merged with the theory of general relativity to produce a so-called "theory of everything". Even though Einstein's theory predicts gravitational waves, this radiation has not been directly observed.

Related Topics:
Open problems - N-body problem - Classical mechanics - Quantum mechanics - General relativity - Theory of everything - Gravitational wave

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