Abstract
I. ALTHOUGH the observations made by Fraunhofer in 1814 first indicated that the spectra of stars were not all of the same character, it was the more systematic observations of Rutherfurd and Secchi fifty years later which revealed the fact that the different varieties of stellar spectra were, generally speaking, associated with stars of different colours. The stars with fluted spectra, for instance, were generally found to be red; those resembling the sun in having abundant metallic lines were yellowish; while those in which the chief absorption was due to hydrogen were white. Closely following these observations came Zöllner's suggestion that the spectra mieht indicate the relative ages of the stars, and that the yellow and red stars were older and cooler than the white ones, thus giving birth to the now generally accepted view that the different kinds of stellar spectra represent different temperature stages in the evolution of more or less similar masses of matter. More direct evidence as to temperature differences was brought forward shortly after by Lngstrom, who directed attention to the probability that the flutings characteristic of the red stars originated in chemical compounds, and pointed out that the occurrence of flutings in such a star as Betelgeuse might be taken as an indication that the temperature of the star was sufficiently reduced to permit the formation of chemical combinations. Subsequent researches have shown that all flutings do not proceed from compounds, but the fact remains that in laboratory experiments flutings are only produced by relatively cool vapours and gases, and their presence in the spectrum of a star may therefore be still accepted as evidence of greatly reduced temperature. The broad distinction between the spectra of cool and hot stars was thus early recognised, but it remained to establish the sequence of temperature in the stars characterised by line spectra.
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References
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FOWLER, A. The Classification of Stars According to their Temperature and Chemistry . Nature 70, 611–614 (1904). https://doi.org/10.1038/070611a0
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DOI: https://doi.org/10.1038/070611a0