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

1;58 Tr1, MtooN.
The1I semi-fanglk of the openumbra lt11 l ): 1BI81)lSl-.R., of
which BSI) the stin's horizontal parallax at tlhe moow0^n:.':".5,
alnd 8131t the sun's apl)]arentt se39i-dialcdter::l' 3".9 anld
hence 1lI1) is known. The moonh's apparentl semi-diameter
1(-:..)::. G' t4-5".5.'llerefore GDT is klnown, as likewise 1)1
andl'iG-. Ience the angle (Td mnay be found, and the are dG(
and its dol.ble (Gl, which equals tle angulalr 1breadth of the
penumbra It may be converted into miles by stat ilng a pro})ortion a,; in article 2,66. On malking the cealculation it will
be found to be 4:393 miles.
268.'T'llc apparelnt diameter of thle moon is solmetimes
lartg-'r tllan that of the sun, sometimes s8m1aller, and somletimess
exactlyr equal to it. Suppose an observer placed on ttm rigitt
line which joins the center1' of tll Sun and moon ll; it' tfc app.'enit dialmeter of the moon is greater than thallt of tlhe stmn,
thie eclipse will be total. If thle two dialneters are equal, the
mool's shaldow just reaches tie eartlh, and tile sun is lhidd(le
but for a moment. fiom the viesw of spectators situated in the.........
~-;....................................~.'.'..... -'.:-......:. - v::::........'...-........;::. V..;,, - -
line which the vertex of the sfiadow (lescriibes on the surfa'ce of
the earth., lut if, as hlallpens wihen tlie moon comnes to her
coiljmiction in tllat part of 1her orb1 it whllil s tow aid her apocc, thle tonll's dliamleter is less than tlhe sutl's, t lhen te ob