Page:Astronomy for Everybody.djvu/164

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THE SUN, EARTH, AND MOON

the moon appears a little the larger, and sometimes the sun. In the former case the moon may entirely hide the sun; in the latter case she cannot do so.

One important difference between an eclipse of the moon and of the sun is that the former is always the same wherever it is visible, while an eclipse of the sun depends upon the position of the observer. The most interesting eclipses are those in which the centre of the moon passes exactly over that of the sun. These are called central

Fig. 26.—The Moon Passing Centrally over the Sun during an Annular Eclipse.

eclipses. To see one, the observer must station himself at a point through which the line joining the centres shall pass. Then if the apparent size of the moon exceeds that of the sun, the former will completely hide the sun from view. The eclipse is then said to be total.

If the sun appears the larger, a ring of its light will surround the dark body of the moon at the moment of central eclipse. The latter is then called annular (Latin annulus, a ring).

The line of centres of the two bodies sweeps along the surface of the earth, and its course may be shown by a line marked on a map. Such maps, showing the regions

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