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

ANN UAt MO3IOTI ON.
when tlle sulln is present, vtet -after the sunll is set, we can o.bserve that it; make.s daily progCress eastward, as is appalent
friom the constellaitions of the Zodiac occupying, sulecessi vely
tlthe western sky after sunllset, provin tlhat either all tilhe stars
have a couinnllll motion westwhard iltdepenldent of tlheir diurnal
mlotion, or tlhat tle sun has a,motiont past thlcm, fromn west. to
east. rWe shiall see lhereafte allundant evidence to prove that
this ctang in tlle relative positio:l of the sulll and stars, is
owing to ta tparalltic cthalge ill the place of the sun, and not
to anyll chaige ill the stars.
1 54. Altlough the apparentt revolution of thie sun is is ll a
direction opposite to the real motion of the eartht, as regards<
absolute sp-ace, yet both are nevertheless fr'om wezst to east,
since thlese termls (1 not refer to ant directionslfl in absolulte
space, but to the order ill whicht certain constellations (the onllstellat tions of the Zodiac) succeed one anothler. Tlhe earth itself,
oni olposite sides of its orbit, does, in fact, movet toward directly op)posite points of spacet; Iut it is all thle while purs)ll ng
its course in thle order of thle signs. In the sailnme malnnler,
althloulgh tle earth turns on its axis frtom west to east, yet any
place ont the srl'fae of the eartth is moving in a direction in
space exactl y opposite to its di rection twelve lholls tbefotr. If
the sun lelft t visible trace oin the thee of tlle sky, tile eclilt.ic
vould, of courxse, be distincftly marked on thle celestial slhSere
as it is on al artificial gtlobe; and were the equator delinleated
in a similar manner (b1y any method like that supposed il Art.
4), we shiould thelln see at a glance them relative position of
these two cilcles; tlhe points whtre they intetse.ct one another
constitutingl the equinoxes, the points where they are at the
gr'eatest distance asunder, or the solsticet, and v'arious otler
particulars, whlieh, for want of suctll visible t races, we ar'e now
obligedl to s-earch for by indirect and circuitous nmetlhods. It
will even aid thle learner to have constantly before his mental
vision), an imaginary delineation of tlhese two imlpolrtant circles
on tlle face of tlhe sky.
1 5 t.'7l ie etithod of ascertaining the nature andposition qtf
ter tear/it's orbit is by observations on tie sun's Declination Zand
I)litt Asceestot.