. Astronomy for high schools and colleges . al sphere, any change inthe direction of the pole of the earth necessarily changesthe position of the equator among the stars. ISTow thepositions of the celestial pole and the celestial equatoramong the stars seem to remain unchanged throughoutthe year. (There is, indeed, a minute change, but it doesnot affect our present reasoning.) This shows that, asthe earth revolves around the sun, its axis is constantlydirected toward nearly the same point of the celestialsphere. § 5. THE SEASONS. The conclusions to which we are thus led respectingthe real revo
. Astronomy for high schools and colleges . al sphere, any change inthe direction of the pole of the earth necessarily changesthe position of the equator among the stars. ISTow thepositions of the celestial pole and the celestial equatoramong the stars seem to remain unchanged throughoutthe year. (There is, indeed, a minute change, but it doesnot affect our present reasoning.) This shows that, asthe earth revolves around the sun, its axis is constantlydirected toward nearly the same point of the celestialsphere. § 5. THE SEASONS. The conclusions to which we are thus led respectingthe real revolution of the earth are shown in Fig. S represents the sun, with the orbit of the earthsurrounding it, but viewed nearly edgeways so as to bemuch foreshortened. AB GD are the four cardinalpositions of the earth which correspond to the cardinal THE SEASONS. 109 points of the apparent path of the sun already each figure of tlie earth N S \% the axis, iV^ being itsnorth and S its south pole. Since this axis points in the. CAUSES OF THE SEASONS. same direction relative to the stars during an entire year,it follows that the different lines iV^ aS are all , since the equator does not coincide with the ecliptic,these lines are not perpendicular to the ecliptic, but areinclined from this perpendicular by 23-1^°. Now, consider the earth as at A ; here it is seen that thesun shines more on the southern hemisphere than on thenorthern ; a region of 23J° around the north pole is indarkness, while in the corresponding region around thesouth pole the sun shines all day. Tlie five circles at rightangles to the earths axis are the parallels of latitude aroimdwhich each region on the surface of the earth is carried bythe diurnal rotation of the latter on its axis. It Avill be seenthat in the northern hemisphere less than half of these areilluminated by the sun, and in the southern hemispheremore than half. This corresponds to our winter solstice. When the ea
Size: 2138px × 1168px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookpublis, booksubjectastronomy
