Astrophysics (Index)About

emission line

(narrow frequency-region of a spectrum with higher intensity)

An emission line is a spectral line due to emission of electromagnetic radiation from a (thin) cloud of gas with enough atomic excitation that the relaxation of atoms to lower energy levels is a primary source of the radiation it generates (as per Kirchhoff's laws). Such lines are used to identify such gas and analyze its properties: in addition indicating a component of its makeup, redshifted lines help estimate distance or radial velocity.

By contrast, absorption lines are produced when the continuous spectrum produced by a hot body passes through a (relatively) cooler gas. The gas's absorption of the EMR passing through tends to be at wavelengths matching the differences in energy from one atomic excitement level to another.

Further reading:

Referenced by pages:
absorption line
active galactic nucleus (AGN)
Atacama Pathfinder Experiment (APEX)
Balmer series (H)
broad emission line region
Be star
broad-line region (BLR)
Brackett series
brightness temperature (TB)
ionized carbon fine structure line ([CII])
carbon monoxide (CO)
Carbon Monoxide Mapping Array (COMA)
Compton reflection
core collapse supernova (CCSN)
diffuse emission
electron orbital
emission line galaxy (ELG)
emission-line star
emission nebula
star formation feedback
foreground subtraction
Fraunhofer lines
Herbig AeBe star (HAeBe)
HII region (HII)
hydrogen deuteride (HD)
iron (Fe)
Kirchhoff's laws
Lyman-alpha emitter (LAE)
line broadening
spectral line shape
line tomography
Lyman series (L)
molecular cloud turbulence
Molecular Deep Field
non-thermal emission
Paschen series
Palomar Four-filter Survey (PC)
P Cygni profile
redshift (z)
radio galaxy (RG)
Seyfert galaxy (Sy)
star formation rate (SFR)
shell star (sh)
submillimeter galaxy (SMG)
supernova (SN)
spectral feature
spectral line
spectral type
Tully-Fisher relation (TFR)
21-cm experiment
21-cm line
transit spectroscopy
T-Tauri star (TTS)
water lines
white dwarf (WD)
Wilson-Bappu effect
Wolf-Rayet star
Zeeman-Doppler imaging (ZDI)