THE OUTLINE OF HISTORY
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THE EARTH IN SPACE AND TIME
THE earth on which we live is a spinning globe. Vast though it seems to us, it is a mere speck of matter in the greater vastness of space.
Space is, for the most part, emptiness. At great intervals there are in this emptiness flaring centres of heat and light, the "fixed stars." They are all moving about in space, notwithstanding that they are called fixed stars, but for a long time men did not realize their motion. They are so vast and at such tremendous distances that their motion is not perceived. Only in the course of many thousands of years is it appreciable. These fixed stars are so far off that, for all their immensity, they seem to be, even when we look at them through the most powerful telescopes, mere points of light, brighter or less bright. A few, however, when we turn a telescope upon them, are seen to be whirls and clouds of shining vapour which we call nebulæ. They are so far off that a movement of millions of miles would be imperceptible.
One star, however, is so near to us that it is like a great ball of flame. This one is the sun. The sun is itself in its nature like a fixed star, but it differs from the other fixed stars in appearance because it is beyond comparison nearer than they are; and because it is nearer men have been able to learn something of its nature. Its mean distance from the earth is ninety-three million miles. It is a mass of flaming matter, having a diameter of 866,000 miles. Its bulk is a million and a quarter times the bulk of our earth.
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