Abstract
THE two outstanding features that characterise the spectrum of the polar aurora are a set of four well-marked bands belonging to the first negative group of nitrogen, and a strongly denned very narrow spectral line in the green, the wave-length of which, measured by Babcock with a Fabry and Perot inter-ferometer, was found to be 5577.35 ± 0.005 A. Less important features are a set of bands belonging to the second positive group of nitrogen and a miscellaneous, and as yet unidentified, set of sixteen lines or narrow bands. The auroral green line, the identity of which was for long unknown, was shown in 1925 by McLennan and Shrum to originate in gaseous atomic oxygen. This spectral line exhibits great variations in intensity with changing conditions of excitation. Helium and neon when mixed in excess with oxygen enhance the intensity of the line. Argon does the same thing, but to a much greater extent. In 1927, McLennan and McLeod established the identity of the oxygen green line with the auroral green line beyond question, through obtaining 5577.341 A.± 0.004 A. for the wavelength of the former by the use of a Fabry and Perot interferometer.
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The Aurora and its Spectrum1. Nature 122, 38–39 (1928). https://doi.org/10.1038/122038a0
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DOI: https://doi.org/10.1038/122038a0