Astrophysics (Index)About

black-body radiation

(EMR with a characteristic spectrum due to the temperature of a body)

Black-body radiation is a kind of thermal radiation (aka thermal emission, EMR from a body due to its temperature), specifically that from a body that is in thermodynamic equilibrium, which implies a constant, uniform temperature. It is a continuum emission, i.e., producing continuous spectrum, with a specific shaped spectral energy distribution (SED), dependent only on the temperature of the body (a black-body spectrum). The SED is "hill-shaped", its peak at a wavelength calculable from the temperature by Wien's displacement law. Planck's law (Planck function) describes the whole spectrum:

I(ν,T) = 2hν3/c2 × 1/(ehν/(kT)-1)

The black-body spectrum represents an ideal case, given that thermodynamic equilibrium and uniform temperature is never perfect, but all materials produce radiation associated with their temperature. The ideal case and its equation represent a useful first approximation, e.g., for stars' spectra.

The terms Planckian and non-Planckian (NP) are used to describe an EMR source (or its spectrum) as adhering to the black-body spectrum or not. Thermal radiation from optically thin plasma diverges a bit from the black-body spectrum.

Given the temperature-dependent black-body spectrum with its hill and peak, particular bands have some association with the temperature of the source of radiation Given two bodies of different temperatures, the one with a higher temperature has its peak at a shorter wavelength, though despite the different location of the peak, for bodies of a given size, the one with the higher temperature is emitting more energy at every wavelength. Extremely low temperatures produce a peak in the radio band, and extremely high temperatures in the gamma-ray band. Below are the temperature ranges that place the peak (based upon the log of the wavelength) within each EMR band:

temperature range where the spectrum peak falls
below 0.00367 K radio
0.00367-3.67 K microwave
3.67-4893 K infrared
4893-9174 K visible light
9174-367000 K ultraviolet
367000-4×108 K X-rays
above 4×108 K gamma rays

The largely black-body radiation from stars and other such astronomical sources typically peaks in the infrared, visible light, or ultraviolet.


(physics,EMR)
Further reading:
https://en.wikipedia.org/wiki/Black-body_radiation
https://astronomy.swin.edu.au/cosmos/b/blackbody+radiation
http://hyperphysics.phy-astr.gsu.edu/hbase/mod6.html
https://lco.global/spacebook/light/black-body-radiation/
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/01._Waves_and_Particles/Blackbody_Radiation

Referenced by pages:
1.3-mm observation
accretion
atmospheric temperature profile
black body (BB)
brightness temperature (TB)
CMB anisotropies
CMB polarization
cold gas
cold spot
color temperature (TC)
Compton scattering
continuous spectrum
continuum
continuum emission
cosmic microwave background (CMB)
dark matter (DM)
eclipse mapping
emissivity
fluorescence
Hawking radiation
infrared (IR)
infrared excess (IRX)
Infrared Telescope Maffei (ITM)
ionized carbon fine structure line ([CII])
K-line
Kirchhoff's law of thermal radiation
line blanketing
Lyman continuum (LyC)
Mars Observer (MO)
microwave
non-thermal emission
obscured fraction-luminosity relation
OH/IR source
photometric system
Planck constant (h)
Planck function
power law
pulsar (PSR)
Rayleigh-Jeans law
Rosseland mean opacity
SCUBA
secondary eclipse
self-absorption
spectral energy distribution (SED)
spectral index (α)
spectral signature
spectral temperature
spectroscopy
star formation (SF)
star formation rate (SFR)
stellar parameter determination
stellar temperature determination
submillimeter galaxy (SMG)
Sunyaev-Zel'dovich effect (SZ effect)
synchrotron radiation
thermal bremsstrahlung
thermal emission
thermal equilibrium
thermodynamic equilibrium (TE)
ultraluminous infrared galaxy (ULIRG)
Very Small Array (VSA)
Wien approximation
Wien's displacement law
X-ray burster (XRB)
X-ray source
young stellar object (YSO)
Zanstra method

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