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

those wtlich.t are 90~ degrees ftonft thle sutt tl e t-.11aled q.adtt.ttt,; anlld tile poits latl'af w\ay bot\'ween thle s3zygiCs iald (tuadratures are called c/e( nft. It h le circle which di vides tite tllliclttctelled fi'rol tthe unefiiftltened hllernisphl)er of ithc Inocon is
callfed the c~;rc!:.l of/ il!.,Ti' ta/in thl at whlticht divides t:e hemi.ls:picre t.lhat. is tunited towtar-l us f'oii thte olppo)site e is called
thle cuc, if/'t' i:, cdi tlTh d iegre of eca ph.ase oedpends on
tle angle between these circles,'2 1 2. A'.s tlI (l moon is an op)a(quel body of a. spl)]ericf'al figuretl',
antd borrows her liglt fromt t1e sunll it is obvious tllat that
Ihalf only whlic t is toward the sunll e:an be illumntliated..More
or less of tllis side is turned toward. the carth, accordill as
the mnoon is at a. greater or less ctonSgation ft'on the sull.'1f o
rcason of thle dillerent, phises will be becst uinderstood froml a
Fig. 46.
-'-.................
Ii \~z. I. c,t
diagratnl. Therefo re, let, T1 (Ftig. 46) represent the eartlt, and
S t}lc suit. ]'ct A, B, 0, &c., be successiv e positiotts of th e
mIuooli. At A tl e eitire dark sie of t de t oo l being turit edt
toward tlhc earth, tlhi disk would be whloltly invisible. At,,
the circle of thte d{isk cutts otl a stmatll p'atrt of tlte ctnlightct edl
hmtlisplhcre, whttich appears) t iln thie heavens att t5 nltder thlte fthr)ul
of:. a cresceit. At C, the fiBst qtur'ter, the circ.le of tie disk
ctts off hatlf the cemdighftciud hcvtlisplierc, a't(l tle mnon atpl pt)ealrs
d'alw~.4/~otoi:nuc'd at c. I li ike manaier it will be Seenl that tho1
atp)pearaiees preseiited at ].), E, &c.,.imust b o t}uos ) rtepresented at t, c, /: