资料来源 : Webster's Revised Unabridged Dictionary (1913)

Parallax \Par"al*lax\, n. [Gr. ? alternation, the mutual
   inclination of two lines forming an angle, fr. ? to change a
   little, go aside, deviate; ? 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.

   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.

   {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; as, the annual
      parallax of a fixed star.

   {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}, 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.

Horizontal \Hor`i*zon"tal\, a. [Cf. F. horizontal.]
   1. Pertaining to, or near, the horizon. ``Horizontal misty
      air.'' --Milton.

   2. Parallel to the horizon; on a level; as, a horizontalline
      or surface.

   3. Measured or contained in a plane of the horizon; as,
      horizontal distance.

   {Horizontal drill}, a drilling machine having a horizontal
      drill spindle.

   {Horizontal engine}, one the piston of which works
      horizontally.

   {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.

资料来源 : WordNet®

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