“horizon”的概念、定义、翻译、参考文献-科学参考

horizon

Physics

A boundary between regions of space–time in general relativity theory that signals cannot cross. For example, in an event horizon around a black hole any light that is inside the black hole cannot escape across the event horizon (in classical general relativity theory). Horizons also occur in cosmology in models of the expanding universe.

Astronomy

The great circle formed by the intersection of the plane perpendicular to the observer’s zenith with the celestial sphere; also called the astronomical horizon.

Geology and Earth Sciences

1. An informal term used in stratigraphy to denote a plane within a body of strata. This may be at a boundary of lithological change, or commonly the term may refer to a thin, distinctive bed within a lithological unit. See also biohorizon.
2. An interface separating two media with different geophysical properties.
3. In soil, a horizontal layer that can be distinguished from the layers below and (except for the surface layer) above it. Identified by a coding system using a capital letter, sometimes followed by a subscript, such layers are used to diagnose soil types. See soil horizon.

Geography

A distinctive layer within a soil which differs chemically or physically from the layers below or above. The A horizon or topsoil contains humus. Often soil minerals are washed downwards from this layer. This material then tends to accumulate in the B horizon or subsoil. The C horizon is the unconsolidated rock below the soil. These three basic horizons may be further subdivided. Thus, Ah horizons are found under uncultivated land, Ahp horizons are under cultivated land, and Apg horizons are on gleyed land. The B horizons are also subdivided by means of suffixes: Bf horizons have a thin iron pan, Bg horizons are gleyed, Bh horizons have humic accumulations, Box horizons have a residual accumulation of sesquioxides, and Bs horizons are areas of sesquioxide accumulation. Bt horizons contain clay minerals and Bw horizons do not qualify as any of the above. Bx horizons or fragipans contain a dense but brittle layer caused by compaction. C horizons are also subdivided: Cu horizons show little evidence of gleying, salt accumulation, or fragipan; Cr horizons are too dense for root penetration; and Cg horizons are gleyed. Additional suffixes may be used. Some soil scientists use the term D horizon for the consolidated parent rock.
In addition to these soil horizons, other layers are distinguished. Thus, the layer of plant material on the soil surface is classified as: the L horizon (fresh litter); the F horizon (decomposing litter); the H horizon (well decomposed litter); and the O horizon (peaty). A leached A horizon is termed an E horizon or eluviated horizon.

单词	horizon
释义	horizon Physics A boundary between regions of space–time in general relativity theory that signals cannot cross. For example, in an event horizon around a black hole any light that is inside the black hole cannot escape across the event horizon (in classical general relativity theory). Horizons also occur in cosmology in models of the expanding universe. Astronomy The great circle formed by the intersection of the plane perpendicular to the observer’s zenith with the celestial sphere; also called the astronomical horizon. Geology and Earth Sciences 1. An informal term used in stratigraphy to denote a plane within a body of strata. This may be at a boundary of lithological change, or commonly the term may refer to a thin, distinctive bed within a lithological unit. See also biohorizon. 2. An interface separating two media with different geophysical properties. 3. In soil, a horizontal layer that can be distinguished from the layers below and (except for the surface layer) above it. Identified by a coding system using a capital letter, sometimes followed by a subscript, such layers are used to diagnose soil types. See soil horizon. Geography A distinctive layer within a soil which differs chemically or physically from the layers below or above. The A horizon or topsoil contains humus. Often soil minerals are washed downwards from this layer. This material then tends to accumulate in the B horizon or subsoil. The C horizon is the unconsolidated rock below the soil. These three basic horizons may be further subdivided. Thus, Ah horizons are found under uncultivated land, Ahp horizons are under cultivated land, and Apg horizons are on gleyed land. The B horizons are also subdivided by means of suffixes: Bf horizons have a thin iron pan, Bg horizons are gleyed, Bh horizons have humic accumulations, Box horizons have a residual accumulation of sesquioxides, and Bs horizons are areas of sesquioxide accumulation. Bt horizons contain clay minerals and Bw horizons do not qualify as any of the above. Bx horizons or fragipans contain a dense but brittle layer caused by compaction. C horizons are also subdivided: Cu horizons show little evidence of gleying, salt accumulation, or fragipan; Cr horizons are too dense for root penetration; and Cg horizons are gleyed. Additional suffixes may be used. Some soil scientists use the term D horizon for the consolidated parent rock. In addition to these soil horizons, other layers are distinguished. Thus, the layer of plant material on the soil surface is classified as: the L horizon (fresh litter); the F horizon (decomposing litter); the H horizon (well decomposed litter); and the O horizon (peaty). A leached A horizon is termed an E horizon or eluviated horizon.
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