Page:Popular Science Monthly Volume 12.djvu/161

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During its time of greatest observed brilliancy the new star in the Swan was very carefully watched by spectroscopists. The results were in many respects interesting. The star in the Crown had shown the bright lines of hydrogen, superposed upon a faint rainbow-tinted spectrum, which was understood to signify that around a real, though probably a small, sun, some outburst of glowing hydrogen had taken place, the chief part of the star's new light being due to this outburst. The same bright hydrogen lines were seen also in the case of the star in Cygnus. But in addition to them other bright lines were seen, which seemed to be identical with those belonging to the solar sierra (or, as many astronomers unclassically call it, the chromosphere) and corona. This, at least, was the opinion of M. Cornu, of the Paris Observatory. Herr Vogel, who began his observations on December 5th, when the star was between the fourth and fifth magnitude, and continued them to March 10th, when the star had sunk below the eighth magnitude, does not agree on this point with M. Cornu, since aline not agreeing with any known line in the spectrum of the sun's sierra was clearly visible from the beginning in the spectrum of the new star. But the most interesting point in connection with Vogel's observations, confirmed also by Mr. Copeland, at the Dunecht Observatory, and by Mr. Backhouse, of Sunderland, was this: that, as the new star died out, not only did the rainbow-tinted background of the spectrum fade gradually out of view, but the relative lightness of the bright lines steadily changed. At last, on March 10th, very little was left of the spectrum which Cornu and Vogel had seen in December. The blue and violet portion of the spectrum had faded entirely from view, a dark gap had appeared in the green, and a very broad, dark band in the blue. Of the bright lines two only remained. One, the F line of hydrogen, in the green-blue, which had been singularly conspicuous last December, was now faint. The other, in the green, which had been faint in December, was now very bright—in fact, nearly the whole light of the star seemed at this time to come from this bright line.

Now, the changes which had thus far taken place were altogether unlike those which had been noticed in the case of the new star in the Northern Crown. As that star faded from view the bright lines indicative of glowing hydrogen died out, and only the ordinary stellar spectrum remained. In the case of the star in Cygnus the part of the spectrum corresponding to stellar light—that is to say, the rainbow-tinted streak crossed by dark lines—faded gradually from view, and bright lines only were left, at least as conspicuous parts of the star's spectrum. This body, then, did not seem to be returning to the stellar condition at all, but actually fading out into a nebula. Not only so, but the lines which still remained conspicuous last March were lines known to belong to the so-called gaseous nebulae. One of them, that which had been the faintest, but was now the brightest, corre-