Horizon \Ho*ri"zon\, n. [F., fr. L. horizon, fr. Gr. ? (sc. ?)
the bounding line, horizon, fr. ? to bound, fr. ? boundary,
limit.]
1. The circle which bounds that part of the earth's surface
visible to a spectator from a given point; the apparent
junction of the earth and sky.
And when the morning sun shall raise his car Above
the border of this horizon. --Shak.
All the horizon round Invested with bright rays.
--Milton.
2. (Astron.)
(a) A plane passing through the eye of the spectator and
at right angles to the vertical at a given place; a
plane tangent to the earth's surface at that place;
called distinctively the sensible horizon.
(b) A plane parallel to the sensible horizon of a place,
and passing through the earth's center; -- called also
rational or celestial horizon.
(c) (Naut.) The unbroken line separating sky and water, as
seen by an eye at a given elevation, no land being
visible.
3. (Geol.) The epoch or time during which a deposit was made.
The strata all over the earth, which were formed at
the same time, are said to belong to the same
geological horizon. --Le Conte.
4. (Painting) The chief horizontal line in a picture of any
sort, which determines in the picture the height of the
eye of the spectator; in an extended landscape, the
representation of the natural horizon corresponds with
this line.
Apparent horizon. See under Apparent.
Artificial horizon, a level mirror, as the surface of
mercury in a shallow vessel, or a plane reflector adjusted
to the true level artificially; -- used chiefly with the
sextant for observing the double altitude of a celestial
body.
Celestial horizon. (Astron.) See def. 2, above.
Dip of the horizon (Astron.), the vertical angle between
the sensible horizon and a line to the visible horizon,
the latter always being below the former.
Rational horizon, and Sensible horizon. (Astron.) See
def. 2, above.
Visible horizon. See definitions 1 and 2, above.
Source: Webster's Revised Unabridged Dictionary (1913)
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