Untitledsun, in the comet that visits us once in a thousand years, in the starwhose distance is incalculable, and in the great clouds of "fire-mist"that we call nebulæ.In considering the evolution of the stars let us keep two points clearlyin mind. The starting-point, the nebula, is no figment of the scientificimagination. Hundreds of thousands of nebulæ, besides even vasterirregular stretches of nebulous matter, exist in the heavens. But thestages of the evolution of this stuff into stars are very largely amatter of speculation. Possibly there is more than one line ofevolution, and the various theories may be reconciled. And this appliesalso to the theories of the various stages through which the starsthemselves pass on their way to extinction.The light of about a quarter of a million stars has been analysed in thespectroscope, and it is found that they fall into about a dozen classeswhich generally correspond to stages in their evolution (Fig. 21).
This is the end of the preview.
access the rest of the document.