elements of orbit
  • The elements of an orbit are the numbers which define its the size, shape and disposition relative to known reference points. Artificial satellites, planetary satellites and stars in multiple systems can all have the elements of their orbits defined, but they are best explained with reference to solar system objects. Here the elements include the size of the semi-major axis and the orbit’s eccentricity, which give its overall dimensions. Also specified are the orbit’s inclination to the ecliptic, which along with the angle along the ecliptic at which the object crosses it heading north and the longitude of its perihelion, locate the orbit in three-dimensional space. The other elements of the orbit are its ‘period,’ or the time taken for an orbit in relation to the Earth or the stars, and the location of the object along its orbit at a given time, usually the start of a particular year, to allow its location along the orbit to be fixed in time and space. These elements allow the planet or other object to be located on its orbit indefinitely into the past or future providing the orbit does not vary.

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