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

120'1 lS' OtOfI N.
RE:VOLUTl ON' OF'T, MOO1N.T
2 1 3.''e moon, revoves a rot, lite ctartl Hfron es. to east,
mak/nkiqX ter tlire i circt!'t of the heutvns ir abotut 271 — atvfs.
4 S
The plrecise law of the moonhs motions in her r0evolutionl
around( tlte eartlh is ascertainled, as ii tie case of tlhe sitn (\Art.:155), b)y daily o)scervations oin her meridian altitudte and righlt
asteCnsiolt.'thllence are deldulced by calcultation her latitude
anld longitude, froml wtllich we find, that thle lmoon describes
oil ttle cele.stial sphelre a grieat circle of which te eartll is thl
cellter.
T'fhe period of thle mnoon's revolution firom anly poilnt in the
heavens rollunl to thle same point acgain, is calledt a mo/th.. A
sid(ctreal ton t/i is tlle time of, tlhe moon's ptassingi from1 anly star,
intil it returntls to the t,saHme star again. A seynlodiealet m/oltz is
the time fiom o(ne conjunletion or new mlool to alotherll. The1
s.ynlodicat monthl is' )outlt 29 d(ayst, or more exactly, 29d. 12ih.
4tin. (2.8-: -. 9.5) 53 d tys. The sidlereal month is about two days
slorter, beuivg d'h. I3 1m. 711.t:23.31 dlays. As the sun
anld moon airo 1)oth revolvingr in thle same liretctiol, and tIhe
un it s movinttgv nearly ai degree a day, during the 27 days of tlle
10oonI's revolution, the sut Imust hlave moved 27. Now since
the ml)oon( pt a ss ov em 3360 in 27.32, (layt, her aily motion,tmust be 13~ 17'. It must thereforet evidently take about two
(ftys fr llthe moon to overtake tilhe l, sun. e (lili lncce bctwccnl
these two periods 1m1ay, hlowever, ) determined with grealt
exactness. The middle of an eclipse of the sun larks the
time of' conjunli ionl or new moon; and by dividing the inter.
val between any two distant solar eclipses by the number of
revolhitiowns of the moon, or unalieot s, we obtainl thle precis
period of tlhe synodiial monitl. Suppose, ifor exanmple, two
eelip)ses occur at an interval of t1,000 lunations; thenl the whole
nlltml)ber of da:s and par'ts of a d(ay thatt compose tlle interva:
divilded by S,t(} will give tlhe exact time of one lunation.jt
The time off the svynodical monthll being ascertainedl tlte exact
)eriol of the sidereal montlh may be1, derived from it. For the
x tv anid odo;, implllling thlat the t-wo bodies coaine toyeher.
j It. inllitt att 1irst \view.ellt nlecmtss'tr v to knlow ti period of onle nlnation be
folte we could know thle 1nmttbctr of lumttionls in any givel interva ll tis period
is lilown l very tcarly nftun tiLe interval etwteen oneV new maooll and anot-her.