Page:The Music of the Spheres.djvu/29

 The material believed to condense into great hot stars is scattered about in various sections of the sky. This material has somewhat the appearance of a summer-day cloud or an illuminated daub of paint, occasionally as shapeless as a pinch of cotton; however, these objects, called nebulæ, have, as a rule, a definite form, the most common being the 'spiral,' the 'ring' and the 'planetary,' these terms also being the descriptive names of such nebulæ. But most of the nebulæ are not for ordinary folks to see for they lie at such vast distances that they are only visible in a large telescope. Sometimes stars are disclosed enmeshed in nebulous folds or again the nebula is seemingly sprinkled with the gold of stars, and there is one object of this kind that every amateur may locate. This is the Great Nebula of Orion which stretches over the whole of the huge constellation of Orion but is concentrated at the star at the center of the Sword which swings from the Giant's Belt.

The Nebula of Orion may be seen in the south in the wintertime with a comparatively small telescope. With a large telescope it is one of the most beautiful and awe-inspiring sights in all the sky.

One theory of the life cycle of a star has it born "of nebulous vapor and dead as a tiny, shrunken old sun" and thus the order of evolution would be from nebulæ to extinct stars, but some astronomers believe that stars may change back to nebulæ, "thus forming a universe having no beginning and no end".

The earth travels in a long journey around the sun. This was surmised by Copernicus in 1530 and proved by Kepler and Galileo