Can anyone define kelper's law of planetary?
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Kepler’s laws of planetary motion, in astronomy and classical physics, laws describing the motions of the planets in the solar system. They were derived by the German astronomer Johannes Kepler, whose analysis of the observations of the 16th-century Danish astronomer Tycho Brahe enabled him to announce his first two laws in the year 1609 and a third law nearly a decade later, in 1618. Kepler himself never numbered these laws or specially distinguished them from his other discoveries.

Kepler's theory of the solar system.Encyclopædia Britannica, Inc.
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celestial mechanics: Kepler’s laws of planetary motion
) Tycho’s observations were inherited by Johannes Kepler (1571–1630), who was employed by Tycho shortly…
Kepler’s three laws of planetary motioncan be stated as follows: (1) All planets move about the Sun in elliptical orbits, having the Sun as one of the foci. (2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time. (3) The squares of the sidereal periods (of revolution) of the planets are directly proportional to the cubes of their mean distances from the Sun. Knowledge of these laws, especially the second (the law of areas), proved crucial to Sir Isaac Newton in 1684–85, when he formulated his famous law of gravitation between Earth and the Moon and between the Sun and the planets, postulated by him to have validity for all objects anywhere in the universe. Newton showed that the motion of bodies subject to central gravitational force need not always follow the elliptical orbits specified by the first law of Kepler but can take paths defined by other, open conic curves; the motion can be in parabolic or hyperbolic orbits, depending on the total energy of the body. Thus, an object of sufficient energy—e.g., a comet—can enter the solar system and leave again without returning. From Kepler’s second law, it may be observed further that the angular momentum of any planet about an axis through the Sun and perpendicular to the orbital plane is also unchanging.

Kepler's first lawKepler's first law of planetary motion. All planets move around the Sun in elliptical orbits, with the Sun as one focus of the ellipse.Encyclopædia Britannica, Inc./Patrick O'Neill Riley

Kepler's second lawKepler's second law of planetary motion. A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.Encyclopædia Britannica, Inc./Patrick O'Neill Riley

Kepler's third lawKepler's third law of planetary motion. The squares of the sidereal periods (P) of the planets are directly proportional to the cubes of their mean distances (d) from the Sun.Encyclopædia Britannica, Inc./Patrick O'Neill Riley
The usefulness of Kepler’s laws extends to the motions of natural and artificial satellites as well as to unpowered spacecraft in orbit in stellar systems or near planets. As formulated by Kepler, the laws do not, of course, take into account the gravitational interactions (as perturbing effects) of the various planets on each other. The general problem of accurately predicting the motions of more than two bodies under their mutual attractions is quite complicated; analyticalsolutions of the three-body problem are unobtainable except for some special cases. It may be noted that Kepler’s laws apply not only to gravitational but also to all other inverse-square-law forces and, if due allowance is made for relativistic and quantum effects, to the electromagnetic forces within the atom.
LEARN MORE in these related Britannica articles:

celestial mechanics: Kepler’s laws of planetary motion
) Tycho’s observations were inherited by Johannes Kepler (1571–1630), who was employed by Tycho shortly…

astronomy: Kepler
…to the first two of Kepler’s laws of planetary motion, published in Astronomia Nova (New Astronomy,…

principles of physical science: Application of Newton’s laws
Kepler’s laws of planetary motion are just such an example, and in the two centuries after Newton’s Principia…

mechanics: History
…investigations, Kepler discovered the three laws of planetary motion that are still named for him. Kepler’s…

physical science: Astronomy
In 1609 Kepler announced two new planetary laws derived from Tycho’s data: (1) the planets travel around…
MORE ABOUT Kepler's laws of planetary motion
9 REFERENCES FOUND IN BRITANNICA ARTICLES
Assorted References
major referenceIn celestial mechanics: Kepler’s laws of planetary motionastronomyIn physical science: AstronomyIn astronomy: Keplercelestial mechanicsIn mechanics: Historydiscovery and formulationIn Johannes KeplergeometryIn geometry: Pythagorean numbers and Platonic solidsgravityIn gravity: Early conceptsorbit of MarsIn Mars: Early telescopic observationsphysical sciencesIn principles of physical science: Application of Newton’s laws
Kepler's laws of planetary motion
External Websites
Article History
Article Contributors

Kepler's theory of the solar system.Encyclopædia Britannica, Inc.
READ MORE ON THIS TOPIC

celestial mechanics: Kepler’s laws of planetary motion
) Tycho’s observations were inherited by Johannes Kepler (1571–1630), who was employed by Tycho shortly…
Kepler’s three laws of planetary motioncan be stated as follows: (1) All planets move about the Sun in elliptical orbits, having the Sun as one of the foci. (2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time. (3) The squares of the sidereal periods (of revolution) of the planets are directly proportional to the cubes of their mean distances from the Sun. Knowledge of these laws, especially the second (the law of areas), proved crucial to Sir Isaac Newton in 1684–85, when he formulated his famous law of gravitation between Earth and the Moon and between the Sun and the planets, postulated by him to have validity for all objects anywhere in the universe. Newton showed that the motion of bodies subject to central gravitational force need not always follow the elliptical orbits specified by the first law of Kepler but can take paths defined by other, open conic curves; the motion can be in parabolic or hyperbolic orbits, depending on the total energy of the body. Thus, an object of sufficient energy—e.g., a comet—can enter the solar system and leave again without returning. From Kepler’s second law, it may be observed further that the angular momentum of any planet about an axis through the Sun and perpendicular to the orbital plane is also unchanging.

Kepler's first lawKepler's first law of planetary motion. All planets move around the Sun in elliptical orbits, with the Sun as one focus of the ellipse.Encyclopædia Britannica, Inc./Patrick O'Neill Riley

Kepler's second lawKepler's second law of planetary motion. A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.Encyclopædia Britannica, Inc./Patrick O'Neill Riley

Kepler's third lawKepler's third law of planetary motion. The squares of the sidereal periods (P) of the planets are directly proportional to the cubes of their mean distances (d) from the Sun.Encyclopædia Britannica, Inc./Patrick O'Neill Riley
The usefulness of Kepler’s laws extends to the motions of natural and artificial satellites as well as to unpowered spacecraft in orbit in stellar systems or near planets. As formulated by Kepler, the laws do not, of course, take into account the gravitational interactions (as perturbing effects) of the various planets on each other. The general problem of accurately predicting the motions of more than two bodies under their mutual attractions is quite complicated; analyticalsolutions of the three-body problem are unobtainable except for some special cases. It may be noted that Kepler’s laws apply not only to gravitational but also to all other inverse-square-law forces and, if due allowance is made for relativistic and quantum effects, to the electromagnetic forces within the atom.
LEARN MORE in these related Britannica articles:

celestial mechanics: Kepler’s laws of planetary motion
) Tycho’s observations were inherited by Johannes Kepler (1571–1630), who was employed by Tycho shortly…

astronomy: Kepler
…to the first two of Kepler’s laws of planetary motion, published in Astronomia Nova (New Astronomy,…

principles of physical science: Application of Newton’s laws
Kepler’s laws of planetary motion are just such an example, and in the two centuries after Newton’s Principia…

mechanics: History
…investigations, Kepler discovered the three laws of planetary motion that are still named for him. Kepler’s…

physical science: Astronomy
In 1609 Kepler announced two new planetary laws derived from Tycho’s data: (1) the planets travel around…
MORE ABOUT Kepler's laws of planetary motion
9 REFERENCES FOUND IN BRITANNICA ARTICLES
Assorted References
major referenceIn celestial mechanics: Kepler’s laws of planetary motionastronomyIn physical science: AstronomyIn astronomy: Keplercelestial mechanicsIn mechanics: Historydiscovery and formulationIn Johannes KeplergeometryIn geometry: Pythagorean numbers and Platonic solidsgravityIn gravity: Early conceptsorbit of MarsIn Mars: Early telescopic observationsphysical sciencesIn principles of physical science: Application of Newton’s laws
Kepler's laws of planetary motion
External Websites
Article History
Article Contributors
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