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Balmer jump

(Balmer discontinuity)
(abrupt change in stellar spectrum at end of Balmer series)

The Balmer jump (or Balmer discontinuity) is an abrupt change in the intensity of some stars' spectra for wavelengths shorter than the "infinity" end of the Balmer series spectral lines, i.e., 364.6 nm. It occurs when the star is sufficiently hot that hydrogen atoms with electrons at level II are generally being ionized rather than moving to a higher level of atomic excitation. Then, any photon of sufficient energy can be absorbed, i.e., a lowering of the continuum at the above-mentioned wavelength.

Its shape is an indication of the star's density and temperature. The jump is strongest in early stars, e.g., A-type stars.

(stars,spectrum,Balmer series)
364.6nm822THz3.5eVBalmer jump

Referenced by:
Balmer-break galaxy (BBG)
blue horizontal branch (BHB)
spectral feature