# black body

Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to black body: Black body radiation
Black-body radiation curves for different temperatures

## black body

A body that absorbs all the radiation falling on it, i.e. a body that has no reflecting power. It is also a perfect emitter of radiation. The concept of a black body is a hypothetical ideal. The radiation from stars, and their effective and color temperatures, can however be described by assuming that they are black bodies.

Black-body radiation is the thermal radiation (see thermal emission) that would be emitted from a black body at a particular temperature. It has a continuous distribution of wavelengths. The graph of the energy, or intensity, of the radiation has a characteristic shape (see illustration) with a maximum value at a given wavelength, λmax. At lower temperatures the black-body radiation is mainly in the infrared region of the spectrum. As the temperature increases the maximum of the curve moves to shorter wavelengths. Curves at different temperatures follow the relationship

λmax T = 2.9 × 103

where the wavelength is measured in micrometers. This is known as the Wien displacement law. The radiation from a hot black body is greater at every wavelength than the radiation from a cooler black body. The total radiation flux thus increases rapidly with increasing temperature, as described by Stefan's law.

Stefan's law gives the total energy emitted over all wavelengths per second per unit area of a black body. The energy emitted at a particular wavelength by a black body can be predicted from Planck's radiation law. This law was derived by Max Planck from his quantum theory, propounded in 1900. If E (λ,T) is the energy emitted per unit wavelength interval at wavelength λ, per second, per unit area, into unit solid angle, by a body at thermodynamic temperature T , then

E (λ,T) = (2πhc 25)[ehc kT – 1]–1

h is the Planck constant, k the Boltzmann constant, and c the speed of light. Stefan's law and the Wien displacement law can both be derived from Planck's law.

Planck's radiation law describes only the continuous spectrum emitted by a black body. The continuous radiation from a star, as opposed to a black body, does not usually follow Planck's law exactly, although over a broad region of the spectrum the law is a good approximation.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006
References in periodicals archive ?
Refusing to be categorized as that which is beyond comprehension, or something undeserving of it, she revises his conceptions on the limits of Black genius in a language he is able to understand, making the larger case for the Black body as a legible sight.
The intensity value of the uncracked specimen taken at a constant illumination is the initial intensity value incident on the cracked specimen, and the reduction caused by the black body cavity is not applied to this value.
The right cavity shows that the black body has a higher thermal radiation than its surroundings.
The first is that the object absorbs and emits some fraction of all frequencies of radiation; this situation may be further subdivided into the special case where the object is itself a black body such as Planck's particle of carbon which is a perfect absorber and emitter at all frequencies; and the general case where the object only absorbs and emits some fraction above zero but less than unity of every frequency.
But <i>The Help</i> conspicuously dodges the sexual violence black women domestics endured at the hands of white men through its debasement of Minny's black body and the emergence of Miss Celia as Minny's great white savior.
Two-hundred black body bags lined up on Brighton beach in East Sussex by campaigners highlighting Britain's 'shameful' response to the migrant crisis in the Mediterranean Tom
The black body was seen as invasive, unnatural, or natural to a fault, equated with flora and fauna -- the politics of the world have repeatedly been played out upon the black body.
To understand the death of Garner is to grapple with the dense, complex, and relational ways in which Thanatos (the very personification of death) haunts the Black body within a white supremacist America where white bodies matter.
In terms of the Black body as a site of "pathology," one might say, criminal pathology, Johnson argues that, according to this logic, Trayvon Martin "had to be guilty of something - some previous crime or sin or moral slippage." Pulling from his existential phenomenological sensibilities, Johnson writes that "His [Martin's] essence is that of a predator." Martin, in other words, is profiled according to a procrustean gaze, in this case George Zimmerman's, that reduces his ontological complexity to a singular state of being, one that is temporally frozen.
In my book Black Bodies, White Gazes, (2) I point to the middle passage as the crucible in terms of which black identity is marked and the black body is ontologically truncated and returned to itself as distorted and monstrous, thus locating the black body within a context of anti-black racism.
That's in addition to a sports-styled exterior which includes piano black body trim, black door mirror covers, a black radiator grille top, smoked headlamps and black 17-inch lightweight alloy wheels.

Site: Follow: Share:
Open / Close