An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

T1E''IIE SUNI.Let A.1C:) rep'resent the earth's place in different parts of
its orbit, having the stm in the cenltel. JILet A, C, be the position of the earthl at the equinoxes, and IB, 1:), its positions at
tile tro|pics, the axis t-s beinl0g always parallel to itself." At A.
and C tlhe sunl shtines on botl t anlti s;,anI now let tile globe
be turned round on its axis, and the learner will easily conccive that the sunl -will appear to deseribe the cquator, whlich
being bisected by the horizon of every place, of course the (lay
and night will be el qual in all parts of the globe.'1'.Again, at
3, whentl the earth is at the southern tropic, tXhe sun slilnes 230beylond the north pole n, and falls the same distance stlort of
the south pole sx.'The case is exactly reversed whte the earth
is at the ]northern tropic and the sun at the soutlthern. Whilo
the earth is at one of the tropics, at 113 for example, let us conceive of it as turning onl its axis, and \twe shall readily see thlat
all that part of the earth whlich lies withlin the north poltlr
circle will enjoy continual d-lay, while tllat wittin the southt
polar circle will hlave conttinual nighlt, and that all other 1)laces
will have tlheir days longer as they are nearer to the enliglitened pole, aiid shorter as tlhey tare nelarer to the uncl lightelend
pole. T:is figure like1wise shlows the successive positions of
the caartl at acdiilhlrent periodls of the,year, Nwith res'pect to thle
signs, and what molths correspond to particuIlar signs. Tintls
the earth enters- Libra and the sunl Aries, on the 21st of MNTarch,
and oil tle 21.st of June thle carth is just entering Ctapricorll
and the sun Cancer.
161I. Hl4ad the axis of the carthl been perpendicular to the
plane of thle ecliptic, then tlhe sunl would always have alpeared
to move in tlhe equator, the days would everywhere have 1)be
equal to the nighlts, andi thlere could have been no change of
seasonls. OIn tlhe other landi, had the inclination of the ecliptic to the equator been muchlt greater thfan t is, the vicissitudtts
of the seasons would have been prol)ortionally greater than at
present. Suppose, for instant e, t:le quator had been at right
The learner wilt remark that the hemisphere toward n is tabove, and that
towaNvrdl s is below the lplane of the paper. It is im1portant to form a just conception of the position of tile axis with respect to tihe platet of its orbit.
-, At the pole, the solar disk, at the timne of the equinox, appears,bisected by
the hori.zon,