the line or circle that forms the apparent boundary between earth and sky.
2.
Astronomy.
a.
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).
b.
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).
3.
the limit or range of perception, knowledge, or the like.
4.
Usually, horizons.the scope of a person's interest, education, understanding, etc.: His horizons were narrow.
5.
Geology. a thin, distinctive stratum useful for stratigraphic correlation.
6.
any of the series of distinctive layers found in a vertical cross section of any well-developed soil.
Origin: 1540–50; < L horizōn < Gk horízōn (kýklos) bounding (circle), equiv. to horíz(ein) to bound, limit + -ōn prp. suffix (nom. sing.); r. ME orizonte < MF < L horizontem, acc. of horizōn
celestial horizon n. A great circle on the celestial sphere having a plane that passes through the center of the earth and is parallel to an observer's horizon. Also called rational horizon.
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.
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.
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