Cosmology Views

Hydrogen Alpha LINES

The word LINES is capitalized because the word "alpha" applies to more than one hydrogen emission line.

When investigating a number of quasar spectra, I discovered astronomers can use "alpha" to reference 2 different wavelengths from hydrogen.

The hydrogen atom has only one electron but that electron can take multiple energy states. These states are quantized so we call them orbitals and they are explained by a quantized orbital  radius.

The change in energy state and the energy emitted or released with that change are related by the wavelength to the distance change between the orbitals.

from Wikipedia:


 physics and chemistry, the Lyman series is a hydrogen spectral series of transitions and resulting ultraviolet emission lines of the hydrogen atom as an electron goes from n ≥ 2 to n = 1 (where n is the principal quantum number), the lowest energy level of the electron. The transitions are named sequentially by Greek letters: from n = 2 to n = 1 is called Lyman-alpha, 3 to 1 is Lyman-beta, 4 to 1 is Lyman-gamma, and so on. The series is named after its discoverer, Theodore Lyman. The greater the difference in the principal quantum numbers, the higher the energy of the electromagnetic emission.


In physics, the Lyman-alpha line, sometimes written as Ly-α line, is a spectral line of hydrogen, or more generally of one-electron ions, in the Lyman series, emitted when the electron falls from the n = 2 orbital to the n = 1 orbital, where n is the principal quantum number. In hydrogen, its wavelength of 1215.67 angstroms (121.567 nm)

A K-alpha line, or Kα, analogous to the Lyman-alpha line for hydrogen.


The Balmer series, or Balmer lines in atomic physics, is one of a set of six named series describing the spectral line emissions of the hydrogen atom. The Balmer series is calculated using the Balmer formula, an empirical equation discovered by Johann Balmer in 1885.

The visible spectrum of light from hydrogen displays four wavelengths, 410 nm, 434 nm, 486 nm, and 656 nm, that correspond to emissions of photons by electrons in excited states transitioning to the quantum level described by the principal quantum number n equals 2. There are several prominent ultraviolet Balmer lines with wavelengths shorter than 400 nm. The number of these lines is an infinite continuum as it approaches a limit of 364.6 nm in the ultraviolet.

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in brief:

The Lyman series is associated with the n=2 orbital in Hydrogen while the Balmer series is for the n=3 orbital.

Lyman-alpha, Ly-α, Lyman-α, K-alpha, K-α are all 1216 Angstroms.

Hydrogen-alpha,Ba-α, Balmer-alpha are all 6563 Angstroms.

Lyman-beta, Ly-β are 1026 Angstroms.

Hydrogen-beta,Ba-β are 4861 Angstroms.

Rarely encountered:

Lyman-gamma, Ly-γ, are 973 Angstroms (sometimes as 972 like in the attached).

Hydrogen-gamma, Hydrogen-γ, Balmer-gamma are 4340 Angstroms.

A crucial mistake is  mixing Ly-α with Hydrogen-α because these "alphas" are different coming from a different series.

If an astronomer  ever identifies an alpha with a hydrogen spectral line, one must trust the correct alpha was selected and shown.

I recently discovered the attached page which also explains this possible confusion of the named lines, including graphics and a table.

All astronomers must know all these details or their declared red shifts would be wrong. I didn't recognize this alpha situation until recently.

A more energetic quasar will drive the hydrogen atom excitations to their higher energy states.

When comparing spectra from different quasars, either n=1 or n=2 ground energy states are observed for the hydrogen atoms..

If there is a possible mistake with a red shift value, then the spectra should be published so the mistake can be corrected as soon as possible.


Some hydrogen emission line trivia from Wikipedia:

The red H-alpha spectral line of the Balmer series of atomic hydrogen, which is the transition from the shell n = 3 to the shell n = 2, is one of the conspicuous colours of the universe. It contributes a bright red line to the spectra of emission or ionisation nebula, like the Orion Nebula, which are often H II regions found in star forming regions. In true-colour pictures, these nebula have a reddish-pink colour from the combination of visible Balmer lines that hydrogen emits.

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