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See under horizon (def 2b).
the line or circle that forms the apparent boundary between earth and sky.
Astronomy.

the small circle of the celestial sphere whose plane is tangent to the earth at the position of a given observer, or the plane of such a circle (sensible horizon)
Also called rational horizon. the great circle of the celestial sphere whose plane passes through the center of the earth and is parallel to the sensible horizon of a given position, or the plane of such a circle (celestial horizon)

the limit or range of perception, knowledge, or the like.
Usually, horizons. the scope of a person’s interest, education, understanding, etc.:
His horizons were narrow.
Geology. a thin, distinctive stratum useful for stratigraphic correlation.
Also called soil horizon. any of the series of distinctive layers found in a vertical cross section of any well-developed soil.
noun
See horizon (sense 2b)
noun
Also called visible horizon, apparent horizon. the apparent line that divides the earth and the sky
(astronomy)

Also called sensible horizon. the circular intersection with the celestial sphere of the plane tangential to the earth at the position of the observer
Also called celestial horizon. the great circle on the celestial sphere, the plane of which passes through the centre of the earth and is parallel to the sensible horizon

the range or limit of scope, interest, knowledge, etc
a thin layer of rock within a stratum that has a distinct composition, esp of fossils, by which the stratum may be dated
a layer in a soil profile having particular characteristics See A horizon, B horizon, C horizon
on the horizon, likely or about to happen or appear
n.

late 14c., orisoun, from Old French orizon (14c., Modern French horizon), earlier orizonte (13c.), from Latin horizontem (nominative horizon), from Greek horizon kyklos “bounding circle,” from horizein “bound, limit, divide, separate,” from horos “boundary.” The h- was restored 17c. in imitation of Latin.
celestial horizon
A great circle on the celestial sphere having a plane that passes through the center of the Earth at a right angle to the line formed by an observer’s zenith and nadir. The celestial horizon divides the celestial sphere into two equal hemispheres based on the observer’s location, with one hemisphere representing the half of the sky visible to the observer at that location and the other representing the half that is hidden from the observer below the Earth’s horizon. The celestial horizon is used as the reference point in determining a celestial body’s altitude. Also called rational horizon. Compare sensible horizon.
horizon
(hə-rī’zən)

The apparent intersection of the Earth and sky as seen by an observer. Also called apparent horizon.

See celestial horizon.

See sensible horizon.

A specific position in a stratigraphic column, such as the location of one or more fossils, that serves to identify the stratum with a particular period.

A specific layer of soil or subsoil in a vertical cross-section of land.

Geology

A specific position in a stratigraphic column, such as the location of one or more fossils, that serves to identify the stratum with a particular period.

A specific layer of soil or subsoil in a vertical cross-section of land.

Archaeology A period during which the influence of a particular culture spread rapidly over a defined area.

see: on the horizon