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In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity.
Orbits were first analysed mathematically by Kepler who formulated his results in his laws of planetary motion. He found that the orbits of the planets in our solar system are elliptical, not circular (or epicyclic), as had previously been believed.
Isaac Newton demonstrated that Kepler's laws were derivable from his theory of gravitation and that, in general, the orbits of bodies responding to the force of gravity were conic sections. Newton showed that a pair of bodies follow orbits of dimensions that are in inverse proportion to their masses about their common center of massThe center of mass of a group of points is defined as the weighted mean of the points' positions. The weight applied to each point is the point's mass. It is also called the center of inertia . For mass that is distributed according to a density ρ x o. Where one body is much more massive than the other, it is a convenient approximation to take the center of mass as coinciding with the center of the more massive body.Within a planetary systemA planetary system consists of at least one star and various orbiting objects (such as asteroids, comets, moons, and planets). Another name for this collection is solar system not to be confused with the Solar System the planetary system that contains Ear, planets, asteroidAn asteroid is a small, solid object in our Solar System, orbiting the Sun. An asteroid is an example of a minor planet (or planetoid , which are much smaller than planets. The asteroids are believed to be remnants of the protoplanetary disc which were nos, cometHalley's Comet nucleus sunlit from the left. A comet is a relatively small astronomical object similar to an asteroid but composed largely of ice. In Earth's solar system, the orbits of comets may extend past that of Pluto; of the comets which enter the is and space debrisWaste Space debris or orbital debris also called space junk are any of the objects in orbit around Earth created by man that no longer serve any useful purpose. They consist of everything from entire spent rocket stages and defunct satellites to explosion orbit the central starFor alternate meanings see star (disambiguation Hubble Space Telescope of the Sagittarius Star Cloud in the Milky Way Galaxy. A star is any massive gaseous celestial body in outer space. Stars appear as shining points in the nighttime sky that twinkle bec in elliptical orbits. Any comet in a parabolic or hyperbolic orbit about the central star is not gravitationally bound to the star and therefore is not considered part of the star's planetary system. To date, no comet has been observed in our solar system with a distinctly hyperbolic orbit. Bodies which are gravitationally bound to one of the planets in a planetary system, either natural or artificial satellites, follow orbits about that planet.
Due to mutual gravitational perturbations, the eccentricities of the orbits of the planets in our solar system vary over time. Pluto and Mercury have the most eccentric orbits. At the present epoch, Mars has the next largest eccentricity while the smallest eccentricities are those of the orbits of Venus and Neptune.
As an object orbits another object, the periapsis is that point at which the orbiting object is closest to the object being orbited and the apoapsis is that point at which the orbiting object is farthest from the object being orbited.
In the elliptical orbit, the orbited object will sit at one focus; with nothing present at the other focus. As a planet approaches periapsis, the planet will increase in velocity. As a planet approaches apoapsis, the planet will decrease in velocity.
See also: Kepler's laws of planetary motion
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