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Updated: May 8, 2025
By laborious processes of comparison between stellar dark lines and the bright rays emitted by terrestrial substances, he sought to assure his conclusions, regardless of cost in time and pains. He averred, indeed, that taking into account restrictions by weather and position the thorough investigation of a single star-spectrum would be the work of some years.
Thus, by comparing the spectrum of a star alongside a spectrum of hydrogen, we may see all the lines, and be sure that there is hydrogen in the star; yet the lines in the star-spectrum may be all slightly displaced to one side of the lines of the comparison spectrum. If towards the violet end, it means mutual approach of the star and earth; if to the red end, it means recession.
Indeed, the last-named observer recognised nearly all the eighteen lines measured by him in the Nova as characteristic of planetary nebulæ. Of particular interest is the emergence in the star-spectrum photographed by Von Gothard of an ultra-violet line originally discovered at Tulse Hill in the Orion nebula, which is also very strong in the Lyra annular nebula.
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