parallax

Definitions:

  • A change in the apparent position of an object relative to more distant objects, caused by a change in the observer's line of sight towards the object.
  • An apparent displacement of an object observed, due to real displacement of the observer, so that the direction of the former with reference to the latter is changed.
  • In <em>optics</em>, an apparent shifting of the spider-lines in a telescope-reticle as the eye is moved before the eyepiece: it is due to the non-coincidence of the threads with the focal plane of the object-glass.
  • The apparent displacement, or difference of position, of an object, as seen from two different stations, or points of view.
  • The apparent difference in position of a body (as the sun, or a star) as seen from some point on the earth's surface, and as seen from some other conventional point, as the earth's center or the sun.
  • The annual parallax. See annual parallax, below.
  • the greatest value of the heliocentric parallax, or the greatest annual apparent change of place of a body as seen from the earth and sun; it is equivalent to the parallax of an astronomical object which would be observed by taking observations of the object at two different points one astronomical unit (the distance of the Earth from the sun) apart, if the line joining the two observing points is perpendicular to the direction to the observed object. The distance of an astronomical object from the Earth is inversely proportional to the <ex>annual parallax</ex>. A star which has an annual parallax of one second of an arc is considered to be one parsec (3.26 light years) distant from the earth; a star with an annual parallax of one-hundredth second of an arc is 326 light years distant. See <er>parsec</er> in the vocabulary, and stellar parallax, below.
  • the apparent difference in position of an object as seen separately by one eye, and then by the other, the head remaining unmoved.
  • the parallax of a body with reference to the earth's center. This is the kind of parallax that is generally understood when the term is used without qualification.
  • None
  • the parallax of a body with reference to the sun, or the angle subtended at the body by lines drawn from it to the earth and sun.
  • the geocentric parallx of a heavenly body when in the horizon, or the angle subtended at the body by the earth's radius.
  • the apparent displacement in position undergone by an object when viewed by either eye singly.
  • (of an optical instrument), their apparent displacement when the eye changes its position, caused by their not being exactly in the focus of the object glass.
  • the annual parallax of a fixed star.
  • The change of <xref>angular</xref> <xref>position</xref> of two <xref>stationary</xref> points relative to each other as seen by an <xref>observer</xref>, due to the <xref>motion</xref> of an observer.
  • The <xref>apparent</xref> shift of an object against a <xref>background</xref> due to a change in observer position.
  • The angle of seeing of the <xref>astronomical unit</xref>.
  • the apparent displacement of an object as seen from two different points that are not on a line with the object
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