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before they came out on the other side. The Earth's shadow is much smaller than that of Jupiter, but it is still large enough to swallow the Moon entirely. On the other hand, when the Moon comes between the Earth and the Sun, its shadow cannot swallow the Earth at all, it can only at best make a little dark patch upon it; if you can get within that dark patch you will see a total eclipse of the Sun, but it may not be easy to get there. The patch does not stay in one place all the time because the Moon is continually moving, and the Earth also is turning on its axis; the patch, therefore,

Fig. 75.—A total Eclipse of the Sun.

makes a track on the Earth, and it may interest you to see the way in which these tracks arrange themselves on the Earth as years roll on. The movements of the Earth and Moon round the Sun are of such a kind that after about eighteen years they come back to nearly the same relative positions. If they came back to precisely the same, then, of course, the track would be exactly repeated in the same place; but the repetition is not so exact as this. Moreover, the interval is not eighteen years exactly, but eighteen years ten and one-third days, and the one-third of a day is important, because it shifts the track just one-third of the way round the Earth, You will see how the