# Solid Angle

In geometry, a solid angle (symbol: Ω) is the two-dimensional angle in three-dimensional space that an object subtends at a point. It is a measure of how large the object appears to an observer looking from that point. In the International System of Units (SI), a solid angle is a dimensionless unit of measurement called a steradian (symbol: sr).

A small object nearby may subtend the same solid angle as a larger object farther away. For example, although the Moon is much smaller than the Sun, it is also much closer to Earth. Therefore, as viewed from any point on Earth, both objects have approximately the same solid angle as well as apparent size. This is most easily observed during a solar eclipse.

### Other articles related to "angle, solid angle, solid angles":

Etendue
... how "spread out" light is in area and angle ... From the source point of view, it is the area of the source times the solid angle the system's entrance pupil subtends as seen from the source ... From the system point of view, the etendue is the area of the entrance pupil times the solid angle the source subtends as seen from the pupil ...
Planck's Law - Introduction
... a unit area of the radiator into unit solid angle within a frequency band of unit width centered on frequency ν ... This nominal meaning is however inaccurate because the radiation varies with both angle and frequency ... It is made precise by shrinking unit area, unit solid angle, and unit bandwidth to their infinitesimal counterparts dA, dΩ, and dν ...
Spectral Flux Density - Flux Density of The Radiative Field At A Measuring Point - Vector Definition of Flux Density - 'full Spherical Flux Density'
... frequency, denotes a variable unit vector with origin at the point, denotes an element of solid angle around, and indicates that the integration extends over the full range of solid angles of a sphere ... Mathematically, defined as an unweighted integral over the solid angle of a full sphere, the flux density is the first moment of the spectral radiance (or specific ...
Solid Angles in Arbitrary Dimensions
... The solid angle subtended by the full surface of the unit n-sphere (in the geometer's sense) can be defined in any number of dimensions ... One often needs this solid angle factor in calculations with spherical symmetry ...
Intensity (heat Transfer)
... intensity of radiation is a measure of the distribution of radiant heat flux per unit area and solid angle, in a particular direction, defined according to where is the ... defined to exclude the effect of reduced view factor at large values note that the solid angle corresponding to a hemisphere is equal to steradians ...

### Famous quotes containing the words angle and/or solid:

Modesty is the only sure bait when you angle for praise.
Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)

London ... remains a man’s city where New York is chiefly a woman’s. London has whole streets that cater to men’s wants. It has its great solid phalanx of fortress clubs.
Louis Kronenberger (1904–1980)