It may seem curious at first sight that the moon, which is very small compared with the sun, should have power to cover the sun. But remember the difference of the distance. The sun is very far, and the moon is very near. Any small object very near will easily hide from your sight a large object at a considerable distance. You may hold up a shilling-piece at arm’s length, and make it cover from sight a man, or even a house, if the latter be far enough away. The sun at a distance of ninety-three millions of miles, and the moon at a distance of two hundred and forty thousand miles, have to our vision the same seeming size. So, when the moon glides between, her round face just about covers the sun’s round face. If the moon were traveling exactly in the same plane as the plane of the earth’s orbit, an eclipse would be a very common affair indeed. But the plane of the moon’s orbit being not quite the same as the plane of the earth’s orbit, she passes sometimes a little above, and sometimes a little below, the exact spot where she would hide the sun’s rays from us. Now and then, at certain intervals, she goes just between. And so well is the moon’s path in the heavens understood that astronomers can tell us, long years beforehand, the day and the hour an eclipse will take place. An eclipse of the sun is sometimes partial, sometimes total, sometimes annular. In a partial eclipse, the moon does indeed pass between, but only so as to hide from us _part_ of the sun. She is a little too low, or a little too high, to cover his face. In a total eclipse, the moon covers the sun completely, so that for a few minutes the bright photosphere seems blotted out from the heavens, a black round body, surrounded by light, taking its place. In an annular eclipse, the moon in like manner crosses the sun, but does not succeed in covering him entirely, a rim of bright photosphere showing round the black moon. For in an annular eclipse, the moon, being a little farther away from the earth than at the time of a total eclipse, has too small a disk quite to hide the sun’s disk. The blackness of the moon during an eclipse is caused by the fact that her bright side is turned towards the sun, and her dark side toward us. An eclipse of the sun can take place only at new moon, never at full moon. At her full, the moon is outside the earth’s orbit, away from the sun, and can not by any possibility pass between.