The Moon

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."

月球

我們發現月球距離地球約23萬9千英里（38萬4千551公里）。月球與地球總保持這個距離，變化不超過兩三千英里。雖然它離地球的距離仍然是那么遠，但是它運轉的方向卻不斷地在變。我們發現月球環繞地球的軌道總是圓周形--或很近似圓周形。每一個月，或者更確切些說是每27又1/3天就環繞地球轉一圈。在太空中月球是我們最近的鄰居。正像我們本身擺脫不了地心吸引力一樣，月球也擺脫不了地球的吸引力。

除了太陽而外，月球好像天空中最大的天體了。可是實際上它卻是最小的天體之一。只是因為它距離我們太近了，所以看起來才顯得大。月球的直徑只有2160英里（3389公里）僅僅比地球直徑的1/4稍多一點。

每一個月或者更精確些說每29又1/2天有一次有個我們稱之為"望月"的時候。這個時候整個月亮的園盤看起來很明亮。在其他一些時候，月亮的園盤只有一部分看起來覺得亮。我們總是發現這亮的部分是面向著太陽的、面背著太陽的那一部分看起來就黑暗。如果畫家們能記住這一點，即只有被太陽照射得發高的那部分月球是明亮的，那他們作起畫來就會畫得更好。這就表明了月球本身是下發光的。月球就像懸在畫龍點睛的一面巨型的大鏡子一樣，它只能反射出太陽光。

但是月球表面上黑暗的部分并不上絕對黑的。一般地這一部分也能有足夠的光讓我們能勉強剛剛能看清月球的輪廓，這就是我們所說的"新月抱著舊月"的現象。我們用來看到舊月輪廓的光并汪是來自太陽，而是來看地球。我們都清楚地知道，海水的表面、雪地的表面，甚至下雨天的路面都會把很強的太陽光反射到我們的臉上，照得我們很不舒服。同樣道理，整個地球的表面也足可以讓我們看清月球的輪廓，如果沒有地球的反射光，那月球的這一部分將會是黑暗的。

假定月球上也有居民，他們就會看到，地球也像一面高懸在天空中的巨型的鏡子一樣，反射太陽光到月球上。"月球居民們"也會談到地球光，正像我們地球人談到月亮光一樣。"新月抱舊月"只不過就是月球表面上正處于黑夜的那一部分被地球的反射光反照的結果。同理，月球上的居民偶爾也會看到我們地球一部分完全處在陽光的照射下，而地球的其余的部分只能照到月光；月球的居民們或許也會把這種現象稱作"新地球抱著舊地球"吧。