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 mean the removal of photons from a beam of electromagnetic radiation (e.g., light), e.g., through interactions of photons and 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 concept is 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 makeup, 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)

Referenced by:
absorption coefficient
absorption line
Atacama Desert
atomic excitation
CCAT-prime (CCAT-p)
cavity-enhanced absorption spectroscopy (CEAS)
methylidyne (CH)
ionized carbon fine structure line ([CII])
Compton reflection
continuous absorption
cosmic dust
diffuse interstellar bands (DIBs)
distance modulus (u)
emission coefficient (j)
emission line
Gunn-Peterson trough
Interstellar Medium Absorption Profile Spectrograph (IMAPS)
interstellar medium (ISM)
Kramers opacity law
line blanketing
line broadening
Lyman series
mean free path
Morgan classification
opacity (κ)
optical depth (τ)
oscillator strength
oxygen lines
PHOENIX stellar model
planet structure
quantum number
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
state of excitation
synchrotron radiation
transmission spectroscopy
water lines