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

)W:Iosl PSES.: 145
dimensions of the shiadow lnst be afifected by several circumnstances; that tlle shadow must be of the greatest lengthl and
breadthl whlen the sun is furtllest from tle ecarth; thllt its
figullre will 1)e slightly modificed by the spheroidal figure of tho
earlltl; and that the moon, l)eilng, at the time of its opposition,
sometines ncearc to the enarth l and solmetilcs fiurtlher firoml it,
will accordingly traverse it at points wtlore its brcadthl varies
more or less.
247. Tlhe semi-man2gle of the cone of the earth.'s shadow is
eq~ual Io the sn's aptrent semi-diameter, mmitnu is is horitzontal.t1at raI..Let AS (Fig. 51.) be the semi-diameter of thle sunl, 1,L
that of the eartl, a:1nd ]i.,O thlle axis of the cartl's shladow.
Then the semi-ang le of the cotne of the cartlh's shadow
Fig. 61.
AI
— fOB AES -.t. A 1..: 3, of wN hich.A. ES is tlle sun's semi-diametcr, and 1:A l his liorizontal pinallax;tad a as botlh these qula,tities are known, lence the anglle a't the vxrtex of thte shadow
becomes known..'uttinl; d foir the sun's somi-diamleter, and1( p
for hlis horizontal parallax, Nvwe have tlc semli-a'ngle of the earth's
slladow u [iC13........
248. A.l the meatn distance of the ferth f'om the subn, the
lengyth, q/? the earth's shadlozo is about 860,000 mniles, orl morso
thant th'ree times the (dista-nce qfl the moon from the eCartf.
In the riguht-angled triangle E1(3, rightt angled fat 13, thlo
alngle LJl being known 1, and the side EI13), we can find the sido
l ~EOC~. For s~in (6 -yJ L II t ): E- This valuo
0ill(4
will vary withf the sun',s semi-diamcter, bhie- greater as that
is less. Its mean value being 1' 1".5, tand the sun's horizol