With the exception of the star or sun around which the earth and the other planets of our solar system whirl, all the other suns are so immensely remote from the earth that their huge diameters dwindle to a mere twinkle of light. The diameters of some of the stars have been measured and have been found to vary from a few thousand miles to many million miles. Our sun, a most medium sized star, has also been measured and has a diameter of 866,000 miles; this diameter, as seen from any other system of planets, would also dwindle to a twinkle, and our great sun would thus be lost among the other stars.
Throughout the sky are young stars, adult stars, and stars whose light has almost flickered out, for stars, we find, even as all other things in Nature, have a limited span of life. This life may last for untold ages but as surely as stars are formed, so do they die.
The nucleus of a star is formed by gas under high pressure. This gas is gathered together by the force of gravity and gradually condensed into a glowing ball. In contracting the stars at first rise in temperature but when too advanced condensation retards this contraction, then the star gradually cools.
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.
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."