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

112 Tr:LTe SUN.
elrly bodyv, in order to obtain its true place, are callel l'- atiofns.'l'tus tile elliptical fiorm of tlhe cartll's orbit, tlthe prcccssion of
ttc equinoxes, antld the nutation of the earth's axis, severally
affkct tllhe 1lace of' the sunl in his apparent orbit, fbr whichl
eqttuations are tp)licd. In a collection of A.tstronomlincal Tables,
a larlg 1partt ol' the whole are devoted to thliS object.'l}t1cy give
uls thle amlount of the corrections to be <lapplied under all the
circumlstanceiecs and constantly vary)ling relations in whlichl the
811lu, lmoot11 anld elarth are situated( witll respect to eaclt otlher.
I'te antigular distance of tlhe eartht or ally tlatet t from its pec'ibeclioll, oil thie tl)position l tl-t. it tnov-es ttniibrnl' ill a circle,
is called its./can Aot,:!/: its, actual distance at the santl: —momltent inl its orbit is called its Y'PT7e A.o/malZy.'Tllus in figture 44, lt A t El? repres- ent the orbit of thle earth
ltaving'r tile sull int oie of tle foci at S. 1lpon A. P desribe tdle
circle AMPtt1. b: et fE be tihe plaee of the earth inl its orbit, and
A.t thle correspolldilngl place ill thle circle; ei. 4.
thellct tdil angle iO(P1. is tile iealln,t( -.
S.S thl)e t-l re atlcl-ttomaly. Tll tdifference,:''
between tle l tn an td true aloinlSy /,
tSf:'i:MC:', is called fl/e.Iy:uato o'/n
flae Gaer, be-il that correction whichs.
depends oni the elliptical firm of tlhe orbit, or on t le distallce of the centlr of
att'action fl',:,nl tIle center of tleC fig llre,
that is, oil t{h, cccentricity of the orb)it. It is ltmuch tliCe gre't —
est of all tlhe corrections used in finttipg the suno's true lonlgitutde, amtounting, at its maximumn to nearly twro degrees (tV
5 5' 2 3".S).
Contsiderino tle mean and true anom-l aly as agreeing at 1,
the title place of the earth t I is in advance of tlhe mean place
t[, beccause tlhe velocity nearl t}tc perihelion is glreater ttlt thlo
lmca velocity. T.h'tis dificrence between tile mean tand true
plXaces (cquationt of tlhe cetltcr), inlccrtases till the eatth hat s advanced about 90~ to tD, when the velocity has reached its mean
value; from t I) to.A, the true place moves slower thtan the mean,
until at A. the gc:tiland los s are balanced, and th}e true atnd
mean gain coincidc.:tlt, as thie ctlrtft's inotiot is now slower
thlan tite averaget, tlhe trt'11e lace falls bhclind t}Ie ctuml, and tloe
equlation is neglative, till the eartht returns to tlte periltlion.