. A complete geography. ope;but the others are easily seen, and Venus is the most brilliant object inthe heavens, after the sun and moon. It appears either as the EveningStar or Morning Star. Find some of the planets in the sky. There is a very close resemblance among the members of this solarfamily. All are spherical in form, and each one, whose movements are known, rotates upon an axiswhile revolving about the sun. Although the earth ismuch nearer the sun thansome of the other planets,its real distance is about93,000,000 miles, and throughall that space the sun sendsboth light and heat (Fig.
. A complete geography. ope;but the others are easily seen, and Venus is the most brilliant object inthe heavens, after the sun and moon. It appears either as the EveningStar or Morning Star. Find some of the planets in the sky. There is a very close resemblance among the members of this solarfamily. All are spherical in form, and each one, whose movements are known, rotates upon an axiswhile revolving about the sun. Although the earth ismuch nearer the sun thansome of the other planets,its real distance is about93,000,000 miles, and throughall that space the sun sendsboth light and heat ( .-• *T. ^ * iw, • . A ^ 270). Certainly it takes a Notice that of all the rays passing outward from -^ -^ the sun only a very small part reach the earth, tremendoUS body to do this,the rest passing off into space and to other and that fact is clearly sliownplanets. -^ in Fig. 271. Continents and Ocean Basins. — It is believed that all of the planets were once hot bodies like the sun and the stars. The larger. Fig. 270. THE EARTH AS A PLANET 243 planets have not cooled as much as the earth, and some of them seemstill to be hot. For example, the atmosphere of Jupiter is alwaysfull of clouds, as if the heat of theplanet caused the ocean water torise as steam. On the other hand,Mercury, Mars, Venus, and theEarth (Fig. 269), being so muchsmaller, have of course cooled morequickly. They have therefore be-come solid, and a cold crust ofminerals and rocks has formedaround the still heated interior. You will recall (p. 1) that, asthe interior of the earth continuesto cool and contract, the crust Fig. 271. settles upon it and is thus thrown Relative size of earth aud sun. into folds and wrinkles. It is thesegreat upfolds that have formedNorth America and the other con-tinents, while the downfolds haveformed the ocean basins (Fig. ,272). Name the continents andcompare North America in area with each of the others (see Ap-
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