Astrophysics (Index)About

Lyman alpha

(Ly-α, Lyα, Lyman α)
(first line in the Lyman series)

Lyman alpha (Ly-α or Lyα) is a hydrogen spectral line, the first line in the Lyman series and of interest for astronomical observation. It has a wavelength of 121.6 nm, in the extreme ultraviolet (EUV) range (as is the whole Lyman series) and cannot be observed from the ground unless considerably redshifted. Ly-α emission lines in galaxies (Lyman-alpha emitters) are a sign of star formation and at cosmological distances, it a suitable line for determining the galaxy's redshift. It is also used to detect clouds at such long distances by noting the absorption lines in the EMR of quasars at the wavelengths indicating Ly-α various redshifts: the collection of such absorption lines is termed the Lyman-alpha forest. Similarly, the Gunn-Peterson trough is the effects of Ly-α absorption before recombination.

Lyα is also of interest regarding extra-solar planets: detection of absorption lines in the atmosphere through differential spectroscopy allows the spectral line shape to be analyzed, which can reveal whether the velocity is consistent with atmospheric escape.

The term Lyman alpha also applies to corresponding lines of any ion with just one electron. For 4He, the wavelength is less than 1 nm different than that of 1H. (Deuterium's Lyman alpha is also less than 1 nm different.)


(Lyman,hydrogen,line,spectrum)
Further reading:
https://en.wikipedia.org/wiki/Lyman-alpha_line
https://www.chemeurope.com/en/encyclopedia/Lyman-alpha_line.html
https://www.anisotropela.dk/encyclo/lyman_alpha.html
https://www.nist.gov/system/files/documents/srd/jpcrd382009565p.pdf
https://w.astro.berkeley.edu/~jcohn/lya.html
WaveLFreqPhoton
Energy
  
121.6nm2.5PHz10eVLyman alpha

Referenced by pages:
AMUSE²
Cosmic Dawn Intensity Mapper (CDIM)
damped Lyman alpha absorber (DLA)
Dark Energy Spectroscopic Instrument (DESI)
electron orbital
GLARE
Gunn-Peterson trough
intensity mapping (IM)
K-line
Lunar Reconnaissance Orbiter (LRO)
Lyman beta (Ly-β)
Lyman break (LB)
Lyman series (L)
Lyman-alpha blob
Lyman-alpha emitter (LAE)
Lyman-alpha forest
N 103B
oscillator strength
proximity effect
spectral line designation
star formation (SF)
transit spectroscopy
X-SHOOTER Lyman α survey at z = 2 (XLS-z2)

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