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The phrase "spectral lines", when not qualified, usually refers to lines having wavelengths in the visible band of the full electromagnetic spectrum. Many spectral lines occur at wavelengths outside this range. At shorter wavelengths, which correspond to higher energies, ultraviolet spectral lines include the Lyman series of hydrogen.
If the same pattern of intervals is seen in an observed spectrum from a distant source but occurring at shifted wavelengths, it can be identified as hydrogen too. If the same spectral line is identified in both spectra—but at different wavelengths—then the redshift can be calculated using the table below.
Four lines (counting from the right) are formally in the visible range. Lines five and six can be seen with the naked eye, but are considered to be ultraviolet as they have wavelengths less than 400 nm. 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 ...
In 1890, Rydberg proposed on a formula describing the relation between the wavelengths in spectral lines of alkali metals. [2]: v1:376 He noticed that lines came in series and he found that he could simplify his calculations using the wavenumber (the number of waves occupying the unit length, equal to 1/λ, the inverse of the wavelength) as his unit of measurement.
Lines of the spectra of elements could be predicted from existing lines. [ 1 ] [ 2 ] Since the frequency of light is proportional to the wavenumber or reciprocal wavelength , the principle can also be expressed in terms of wavenumbers which are the sum or difference of wavenumbers of two other lines.
The spectral series of hydrogen, on a logarithmic scale. The emission spectrum of atomic hydrogen has been divided into a number of spectral series, with wavelengths given by the Rydberg formula. These observed spectral lines are due to the electron making transitions between two energy levels in an atom.
In the physical sciences, the spectrum of a physical quantity (such as energy) may be called continuous if it is non-zero over the whole spectrum domain (such as frequency or wavelength) or discrete if it attains non-zero values only in a discrete set over the independent variable, with band gaps between pairs of spectral bands or spectral lines.
Therefore, the lines seen in the image above are the wavelengths corresponding to n = 2 on the right, to n → ∞ on the left. There are infinitely many spectral lines, but they become very dense as they approach n → ∞ (the Lyman limit), so only some of the first lines and the last one appear.