Astrophysics (Index)About


(removal of photons from a beam of EMR)

The term absorption is used in the study of radiative transfer and spectroscopy to indicate the removal of photons from a beam of electromagnetic radiation (e.g., light) through interactions of photons with particles such as molecules, atoms, ions, or electrons. In this usage, a photon which is scattered out of the beam is considered absorbed. It is the inverse of emission, the addition of photons to the beam. The two concepts are used widely in astrophysics, for explaining and modeling stars, for dealing with the effects of the Earth's atmosphere, for explaining and modeling gas clouds, etc.

Absorption is complicated by the variety of processes that cause it, and varies by the density, the constituents, and the temperature of the material the beam is passing through. Absorption lines are a result of a type of absorption that is very sensitive to wavelength. A classification of types of absorption is based upon the status of an electron with which the photon is interacting:

The first three have an inverse which constitutes emission. Electron scattering is both absorption and emission, the latter for the beam along the photon's new trajectory.

(physics,EMR,radiative transfer,photons)
Further reading:

Referenced by pages:
absorption coefficient
absorption line
Australian Square Kilometre Array Pathfinder (ASKAP)
Atacama Desert
atomic excitation
Balmer jump (BJ)
Fred Young Submillimeter Telescope (FYST)
cavity-enhanced absorption spectroscopy (CEAS)
methylidyne (CH)
ionized carbon fine structure line ([CII])
Compton reflection
continuous absorption
cosmic dust
chemically peculiar star (CP star)
damping profile
diffuse interstellar bands (DIBs)
diffusion damping
distance modulus (μ)
damped Lyman alpha absorber (DLA)
emission line
emission nebula
free streaming
Gunn-Peterson trough
helium 1083 nm line
Interstellar Medium Absorption Profile Spectrograph (IMAPS)
interstellar medium (ISM)
Kirchhoff's law of thermal radiation
Kramers opacity law
line blanketing
line broadening
Lyman-alpha forest
Lyman series (L)
mean free path
Morgan classification
optical depth (τ)
oscillator strength
oxygen lines
PHOENIX stellar model
planet structure
quantum number
radiation zone
radiative transfer (RT)
redshift (z)
radiative transfer code (RT code)
equation of radiative transfer (RTE)
radiative transfer model (RTM)
source function (S)
spectral band
spectral line
spectral type
state of excitation
synchrotron radiation
thermal bremsstrahlung
transition region
transmission spectroscopy
water lines
Zanstra method