. A complete geography. andlighted for the remainder of the year. Revolution of the Earth around the Sun. — This leads us to thesecond cause for our seasons. Although the earths axis is ahvaysinclined in the same direction, the earth does not always remain onthe same side of the sun ~; for, in addition to its rotation, the earthhas another movement, that of travelling, or revolving^ around thesun (Fig. 277). On this account it does not have the same polealways turned toward the sunlight. Although the sun is ninety-three million miles from us, the earthis moving at such a tremendous rate that i
. A complete geography. andlighted for the remainder of the year. Revolution of the Earth around the Sun. — This leads us to thesecond cause for our seasons. Although the earths axis is ahvaysinclined in the same direction, the earth does not always remain onthe same side of the sun ~; for, in addition to its rotation, the earthhas another movement, that of travelling, or revolving^ around thesun (Fig. 277). On this account it does not have the same polealways turned toward the sunlight. Although the sun is ninety-three million miles from us, the earthis moving at such a tremendous rate that it completes one journey 248 GENERAL GEOGRAPHY around the sun, or one revolution, in almost exactly 365 days, orone year. This explains how we get our year. The other planets require different periods for one revolution. Forinstance, Mercury, which is about 36,000,000 miles from the sun, takesless than three months, while Neptune (Fig. 269), about 2,700,000,000miles distant, requires 165 years for a single Fig. 277. To illustrate the revolution of the earth around the sun. The shaded portion representsnight. The end of the axis around which the earth rotates is the point where the linescome together (the north pole). At what date is this pole turned toward the sun ? Awayfrom it ? Neither towards nor away from it ? What portions of the earth do the sunsrays reach at each of these times ? The Attraction of Gravitation. — In its revolution the earth is movingat the rate of more than one and a half million miles per day. Whatspeed! And at the same time it is whirling or rotating rapidly on itsaxis, as already explained (see First Book, p. 116). THE EARTH AS A PLANET 249 As in tlie case of the earths rotation, one might ask (First Book, ), Why are we not swept from the earth by the wind ? The answer,as before, is that the air, and everything else upon the earth, is drawntoward it and held in place by the force of gravity, so that all traveltogether in the journe
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