Let us now turn to consider the moon; not as the light which makes our nights beautiful, nor as the body which governs the mighty ocean in its tidal sway, but as another world,—the companion planet of the earth.
It has always been a matter not only of the deepest curiosity, but of the greatest scientific import, whether other planets, and particularly our own satellite, are inhabited or exhibit any traces whatever of animal or vegetable life.
One or two astronomers have claimed the discovery of vegetation on the moon's surface by reason of the periodic appearance of a greenish tint; but as the power of the telescope can bring the moon to within only about a hundred and twenty miles of us, these alleged appearances cannot be satisfactorily verified.
The moon is a globe, two thousand one hundred and sixty-five miles in diameter; very much less, therefore, than our earth, which has a diameter of about seven thousand nine hundred and twenty miles.
Thus the moon's surface is less than one thirteenth of the earth's. Instead of two hundred millions of square miles as the earth has, the moon has only about fourteen millions of square miles, or about the same surface as North and South America together, without the great American Islands of the Arctic regions.
The volume of the earth exceeds that of the moon more than forty-nine times. But the moon's substance is somewhat lighter. Thus the mass, or quantity of matter in the moon, instead of being a forty-ninth part of the earth's, is about an eighty-first part.
This small companion world travels like our own earth around the sun, at a distance of ninety-three millions of miles. The path of the moon around the sun is, in fact, so nearly the same as that of the earth that it would be almost impossible to distinguish one from the other, if they were both drawn on a sheet of paper a foot or so in diameter.
You may perhaps be surprised to find me thus saying that the moon travels round the sun, when you have been accustomed to hear that the moon travels round the earth. In reality, however, it is round the sun the moon travels, though certainly the moon and the earth circle around each other.
The distance of the moon from the earth is not always the same; but the average, or mean distance, amounts to about two hundred and thirty-eight thousand eight hundred and twenty-eight miles. This is the distance between the centers of the two globes. With this distance separating them, the companion worlds—the earth and the moon—circle round each other, as they both travel round the central sun.
But now you will be curious to learn whether our companion planet, the moon, really presents the appearance of a world, when studied with a powerful telescope.