Balmerserie

The Balmer-Serie, or Balmer series, is a hydrogen spectral series corresponding to electronic transitions from higher energy levels to the n = 2 level. Photons emitted by these transitions lie predominantly in the visible part of the spectrum, which is why many hydrogen lines are visible in stars and emission nebulae.

The wavelengths of the Balmer series can be described by the Rydberg formula: 1/λ = R_H (1/2^2 − 1/n^2) for n ≥ 3, where R_H is the hydrogen Rydberg constant (approximately 1.097373e7 m−1). This relation explains the discrete lines observed in hydrogen spectra.

The most prominent lines are H-alpha (n = 3 → 2) at 656.3 nm, H-beta (4 → 2) at 486.1 nm, H-gamma (5 → 2) at 434.0 nm, and H-delta (6 → 2) at 410.2 nm. Higher members extend to shorter wavelengths toward the Balmer limit at 364.6 nm, which lies in the ultraviolet.

Historically, the series is named after Johann Balmer, who in 1885 derived an empirical formula for hydrogen line wavelengths. Its theoretical explanation followed from quantum mechanics and the broader Rydberg framework.

Significance: In astronomy and spectroscopy, Balmer lines are used to diagnose physical conditions in stars, H II regions, and galaxies, including temperature, density, and hydrogen abundance. The Balmer decrement helps estimate interstellar extinction, and the lines are commonly used to measure redshifts and to classify astronomical objects.