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3 definitions found
 for Horizontal parallax
From The Collaborative International Dictionary of English v.0.48 :

  Horizontal \Hor`i*zon"tal\, a. [Cf. F. horizontal.]
     1. Pertaining to, or near, the horizon. "Horizontal misty
        air." --Milton.
        [1913 Webster]
     2. Parallel to the horizon; on a level; as, a horizontalline
        or surface.
        [1913 Webster]
     3. Measured or contained in a plane of the horizon; as,
        horizontal distance.
        [1913 Webster]
     Horizontal drill, a drilling machine having a horizontal
        drill spindle.
     Horizontal engine, one the piston of which works
     Horizontal fire (Mil.), the fire of ordnance and small arms
        at point-blank range or at low angles of elevation.
     Horizontal force (Physics), the horizontal component of the
        earth's magnetic force.
     Horizontal line (Descriptive Geometry & Drawing), a
        constructive line, either drawn or imagined, which passes
        through the point of sight, and is the chief line in the
        projection upon which all verticals are fixed, and upon
        which all vanishing points are found.
     Horizontal parallax. See under Parallax.
     Horizontal plane (Descriptive Geometry), a plane parallel
        to the horizon, upon which it is assumed that objects are
        projected. See Projection. It is upon the horizontal
        plane that the ground plan of the buildings is supposed to
        be drawn.
     Horizontal projection, a projection made on a plane
        parallel to the horizon.
     Horizontal range (Gunnery), the distance in a horizontal
        plane to which a gun will throw a projectile.
     Horizontal water wheel, a water wheel in which the axis is
        vertical, the buckets or floats revolving in a horizontal
        plane, as in most turbines.
        [1913 Webster]

From The Collaborative International Dictionary of English v.0.48 :

  Parallax \Par"al*lax\, n. [Gr. ? alternation, the mutual
     inclination of two lines forming an angle, fr. ? to change a
     little, go aside, deviate; para` beside, beyond + ? to
     change: cf. F. parallaxe. Cf. Parallel.]
     1. The apparent displacement, or difference of position, of
        an object, as seen from two different stations, or points
        of view.
        [1913 Webster]
     2. (Astron.) 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.
        [1913 Webster]
     3. (Astron.) The annual parallax. See annual parallax,
     Annual parallax, 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; as, the annual parallax of a fixed star.
        The distance of an astronomical object from the Earth is
        inversely proportional to the annual parallax. 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 parsec in the vocabulary, and stellar parallax,
     Binocular parallax, the apparent difference in position of
        an object as seen separately by one eye, and then by the
        other, the head remaining unmoved.
     Diurnal parallax or Geocentric parallax, 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.
     Heliocentric parallax, 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; as, the
        heliocentric parallax of a planet.
     Horizontal parallax, the geocentric parallx of a heavenly
        body when in the horizon, or the angle subtended at the
        body by the earth's radius.
     Optical parallax, the apparent displacement in position
        undergone by an object when viewed by either eye singly.
        --Brande & C.
     Parallax of the cross wires (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.
     Stellar parallax, the annual parallax of a fixed star.
        [1913 Webster]

From WordNet (r) 3.0 (2006) :

  horizontal parallax
      n 1: the maximum parallax observed when the celestial body is at
           the horizon

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