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单词 parallax
释义
parallax

Physics
  • 1. An apparent displacement of a distant object (with respect to a more distant background) when viewed from two different positions. If such an object is viewed from two points at either end of a base line, the angle between the lines joining the object to the ends of the base line is the angle of parallax. If the base line is the distance between the two eyes of an observer the angle is called the binocular parallax.

    2. The angular displacement in the apparent position of a celestial body when observed from two different points. Diurnal parallax results from the earth’s daily rotation, the celestial body being viewed from the surface of the earth rather than from its centre. Annual parallax is caused by the earth’s motion round the sun, the celestial body being viewed from the earth rather than from the centre of the sun. Secular parallax is caused by the motion of the solar system relative to the fixed stars.


Astronomy
  • The angular difference between an object’s direction as seen from two points of observation; it is thus a form of triangulation. In astronomy, the term is usually taken to mean the difference in position of a celestial object as seen from opposite sides of the Earth’s orbit, which is known as the trigonometric parallax. Parallax can also be defined as the angular distance between two points as seen from a third point in space, such as the radius of the Earth’s orbit as seen from a star. By extension, the term parallax can also be used to mean a star’s distance, even if measured by some indirect method such as photometry (photometric parallax) or spectroscopy (spectroscopic parallax). See also Annual Parallax; Dynamical Parallax; Geocentric Parallax; Horizontal Parallax; Kinematic Parallax; Lunar Parallax; Parallactic Ellipse; Secular Parallax; Solar Parallax; Statistical Parallax.


Space Exploration
  • A change in the apparent position of an object against its background when viewed from two different positions. In astronomy, nearby stars show a shift owing to parallax when viewed from different positions on the Earth's orbit around the Sun. A star's parallax is used to deduce its distance from the Earth.

    Nearer bodies such as the Moon, Sun, and planets also show a parallax caused by the motion of the Earth.


Geology and Earth Sciences
  • The apparent change in position of an object in relation to another when the viewpoint is changed. See also stereoptic vision.


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