An Etymological Dictionary of Astronomy and Astrophysics
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From Johann Jakob Balmer (1825-1898), Swiss mathematician and physicist, who explained the visible spectral lines of the hydrogen spectrum in 1885.

A continuous range of wavelengths in the Balmer spectrum of hydrogen corresponding to transitions between the energy levels n = 2 and n = ∞.

→ Balmer; → continuum.

The intensity ratio among the couple of relatively adjacent → Balmer lines, for example Hα/Hβ and Hβ/Hγ, which have well-known theoretical values. They are used to determine the → interstellar extinction.

→ Balmer; → decrement.

An abrupt decrease in the intensity of the continuum at the limit of the → Balmer series of hydrogen (at about 3650 Å), caused by the energy absorbed when electrons originally in the second → energy level are ionized. Same as → Balmer jump.

→ Balmer; → discontinuity.

A special solution of the mathematical formula which represents the wavelengths of the various spectral series of hydrogen in which the lower energy level is n = 2.

→ Balmer; → formula.

Same as → Balmer discontinuity.

→ Balmer; → jump.

The wavelength in the blue end of the → Balmer series, at 3646 Å, near which the separation between successive lines decreases and approaches a → continuum.

→ Balmer; → limit.

The → spectral lines making up the → Balmer series.

→ Balmer; → line.

A series of hydrogen → spectral lines (Hα, Hβ, Hγ, and others) that lies in the visible portion of the spectrum and results when electrons from upper → energy levels (n > 2) undergo → transition to n = 2.
Historically, Balmer emission lines (mainly Hα) from ionized nebulae were first observed by O. Struve and C. T. Elvey (1938, ApJ 88, 364). This was an important indication of the existence of hydrogen, in the ionized state, in the → interstellar medium.

→ Balmer; → series.