Recent studies have revealed the fact that stars when young are huge and red. This early stage is called the giant stage. Antares, Betelgeuse, Arcturus and Aldebaran are examples of stars at the beginning of their careers. The giant red stars are gaseous throughout and of enormous volume--Antares, the youngest and by far the largest of the four named above, being 400,000,000 miles in diameter. The bluish stars are the hottest stars; a red tinge indicates comparative coolness whether the star is young or old. The blue stars are in the prime of life, intensely hot and brilliant, and glow with a temperature of perhaps 10,000 degrees at their luminous surfaces. With a gradual rise and fall of temperature, stars burn, even as earthly flames, through a continuous series of colors,--generally speaking, red, yellow, blue, yellow, red,--all of which bear a special meaning to an astronomer. The yellow stars, like our sun, are middle-aged; the dwarf red stars, old, like a dying ember. After a star has expended its heat, if it does not in the meantime meet with some accident, it becomes a darkened, lifeless and cold-surfaced globe. [Figure 03: AN IRREGULAR NEBULA IN SCUTUM SOBIESKI. Photograph by Mount Wilson Observatory through 60-inch reflecting telescope.] 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. "I never gazed upon it but I dreamt Of some vast charm concluded in that star To make fame nothing." --_Tennyson_. 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".