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

RY lIV o'ir'T I s. 123
\ltcnw tlhe ascending odef is at th1le verntal equinox, thte
angle of tile mol10l's pathl \witlh tlc hlorizonl'at the tihle of risiil:,.
is 10 l-smaller tlIhan when the descending node is tfl're; and tile
intcrvals va lry according ly. hll:is ioccurs oInce in abolt 1.8 yeaCrs.
22117. l.7'e moont is. abou.tt J.-.2.,neare:r i o ous twhen nea, r the zcn tfith
than,'tI"tn in 4 tshe hriz.o!n...'lthe horizontal distance O) (I.ig 7) is Fl. 47.
ncarly equa l to A1):A:I)',v}iie;hl is rcat-........
or than (:)iD' by AO. the semi-diamecter of
tile earthlt:-,lo- the distancte of thle mlotol.
Accordl',ugl'y, fle t apparent dilameter of the.....................
loo1100 w}hen acttally mettIsuredl is a)bout J.
30'" (w\liclt equals about t-,) of the \whole) greate r wltn in tle
zenith1 titanl ill the 1torizoln. The apparent enlargcemct. of tlle
fill nmoont wlhelt risilg, is owin to tite samtre e;auses as t.hat of
the sunil as cxplaitnedt in article 90.
2 1 t..77e ioon tu.rnts on it/s ax:s in the samtme itt;te in,,wlh.ih,;t re-tivo[ves arou.ndi the ear/it.
Thils is kinowln bly tlhe rmoon's always keepiig nearly tle
same face towatrd us, as is indicated 1by the telsco lpe, whi1
could (not ftappeln unless her revolution on eris kcxeplt Ipace
wvit lther motion in her orbit. llThus, it will be seen by ispectillg filtil'e 31. tlt thle carthl turtns difl'crent faeet tow'ard
the sun at liflerent times; and if a b)all hlaving Oline lltisphere whlite and tlle otlelr black.e carried around a lanmp, it 4
will easily b)e seen that it cannot present thte same face cotstautly toward t he lail) unless it turns oncem oil its axis whlile
perirt'mling its revolution. But thlolughl thte sa1me side of' thte
moon olt thI/e whole a is always toward tie carth, yet thcre are
small appatrent oscillations, by wheicht narrow portionsl of thil
remote side are presented alternately to view. Thuese are
called tibya/zliotzs.
2 1 9. One i' the libtration it t longittde, becatuse it brings
into view portions of thefl equator on one side -land then onl thlo
tlucer. Ilt is owinlg to the fact that the mnoon revolves uniformlv'll1t its axis, and withl lmlqua:l angular nmotion aroulld
thet eartt. Near the apogee, twhere she -advances slowest, she