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The Moon
月球

We find that the moon is about 239,000 miles (384,551 km) away from the earth, and, to within a few thousand miles, its distance always remains the same. Yet a very little observation shows that the moon is not standing till. Its distance from the earth remains the same, but its direction continually changes. We find that it is traveling in a circle - or very nearly a circle - round the earth, going completely round once a month, or, more exactly, once very 27 1/3 days. It is our nearest neighbour in space, and like ourselves it is kept tied to the earth by the earth's gravitational pull.

Except for the sun, the moon looks the biggest object in the sky. Actually it is one of the smallest, and only looks big because it is so near to us. Its diameter is only 2,160 miles (3,389 km), or a little more than a quarter of the diameter of the earth.

Once a month, or, more exactly, once every 29 1/2 days, at the time we call "full moon," its whole disc looks bright. At other times only part of it appears bright, and we always find that this is the part which faces towards the sun, while the part facing away from the sun appears dark. Artists could make their pictures better if they kept this in mind - only those parts of the moon which are lighted up by the sun are bright. This shows that the moon gives no light of its own. It merely reflects the light of the sun, like a huge mirror hung in the sky.

Yet the dark part of the moon's surface is not absolutely black; generally it is just light enough for us to be able to see its outline, so that we speak of seeing "the old moon in the new moon's arms." The light by which we see the old moon does not come from the sun, but from the earth. We know well how the surface of the sea or of snow, or even of a wet road, may reflect uncomfortable much of the sun's light on to our faces. In the same way the surface of the whole earth reflects enough of the sun's light on to the face of the moon for us to be able to see the parts of it which would otherwise be dark.

If there were any inhabitants of the moon, they would see our earth reflecting the light of the sun, again like a huge mirror hung in the sky. They would speak of earthlight just as we speak of moon-light. "the old moon in the new moon's arms" is nothing but that part of the moon's surface on which it is night, lighted up by earth light. In the same way , the lunar inhabitants would occasionally see part of our earth in full sunlight, and the rest lighted only by moon-light; they might call this "the old earth in the new earth's arms."

我们发现月球距离地球约23万9千英里（38万4千551公里）。月球与地球总保持这个距离，变化不超过两三千英里。虽然它离地

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