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单词 orbit
释义
orbit

Physics
  • 1. (in astronomy) The path through space of one celestial body about another. For one small body moving in the gravitational field of another, the orbit is a conic section. Most such orbits are elliptical and most planetary orbits in the solar system are nearly circular. The shape and size of an elliptical orbit are specified by its eccentricity, e, and the length of its semimajor axis, a (see ellipse).

    2. (in physics) The path of an electron as it was envisaged to travel round the nucleus of an atom in the Bohr theory (and extensions of the Bohr theory). See orbital.


Mathematics
  • For a group action G on a set S, the orbit of s ε‎ S is the subset {g·s | g ε‎ G}. The orbits partition the set S.

  • The path traced out by a body experiencing a central force, such as the gravitational force associated with a second body. When the force is given by the inverse square law of gravitation, the orbit is either elliptic, parabolic, or hyperbolic, with the second body at a focus of the conic.


Astronomy
  • The path of a body around another in space. Planets moving around the Sun, and large satellites moving around planets, follow orbits that are approximately ellipses, governed by Kepler’s laws. Other possible orbital shapes are a parabola and a hyperbola. The size and shape of an orbit is defined by its elements (see Elements, Orbital). The changes in those elements with time due to perturbing forces such as the gravitational influence of other bodies can be predicted by celestial mechanics.


Space Exploration
  • The path of one body in space around another, such as the orbit of the Earth around the Sun or of the Moon around the Earth. When the two bodies are similar in mass, as in a binary star, both bodies move around their common centre of mass. The movement of objects in orbit follows Kepler's laws, which apply to artificial satellites as well as to natural bodies.

    As stated by the laws, the orbit of one body around another is an ellipse. The ellipse can be highly elongated, as are comet orbits around the Sun, or it may be almost circular, as are those of some planets. The closest point of a planet's orbit to the Sun is called perihelion; the most distant point is aphelion. (For a body orbiting the Earth, the closest and furthest points of the orbit are called perigee and apogee.)


Chemistry
  • The path of an electron as it travels round the nucleus of an atom. See orbital.


Geology and Earth Sciences
  • 1. The bony socket of the eye.

    2. The path described by a body moving around another under gravitational attraction. See equatorial orbit; geostationary orbit; geosynchronous orbit; low earth orbit; polar orbit; sun-synchronous orbit.


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