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.
[13]
