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

J:cLr. rs1<s.:1.59
server will see a ring of the sun encil'cl the me oon, Collstitutillg anllnnular cclipse. (Fig. 55'.)
26(9. ]Eclipses of tle slunl are modified by the elevatiol of
the moon above the horizon, since its apl)arent d(iamleter is
augmlented as its altitude is itcreased (Art. -2:1). h''11is effect,
comlbined Nwith that of parallax, may so increase or diminishl
the applarent distance between the centers of the suni and
1moonl1 thlat friom thfis cause lollne, of two observers at a distance from each otlher, one might see an eclipse \whlich as not
rvisible to the other. Iff the horizontal liamneter of tlte moon
diflers but little fiom the apparent diameter of the slun, the
case might occur Nwhere the eclipse would be annular over the
places whellcre it was observed morning) and evening, l1ut total
where it was observed at mid-day.
The earthllin its diurnal revolution and the moon's slhadow
)otlt move from west to east, blut tile shadlow moves Pi(ster
than the carthl; h1ence tle moon overtakes thle sml onl its
Nwestern limnb antd crosses it fiom vlest to east,. The excess
of the appalrent diamneter of the moon above that of the
sunll in a total eclipse is so sn1all, that total (larklness seldom
continues longer than four nmittes, and can never continulti
so long as eight mintlts..n annlular eclipse may last:t%.2m 24s,
Since the sunm's ecliptic limIits 1are more than:1tL7 and tlot
moon' s less tfllanl 12~, eclipses of the sunl are more frequent than
those of tie mloon. Yet luntar eclip)ses being visible to eve.ry
part of thle terrestrial hemlisptere opp)1osite to the sun, whlile
those of the sllun arlie visible olnly to the small p)ortion of thte
hemisphrl)e oil wllich the mloonh's shladow fallfs, it halppens that
for any particular place on the carth, lunar eclipses 1are more
firequently visi!ble thlan solar. In any year, thle numtber o'
celipscs of botht luminaries can not be less tthan twvo nlor more
than seven: thle most usual number is fllur, and it is very rare
to have more thtan six. Thet sunll does rnot remain lon I enoIugIt
near a node for the moon to be in syzyg'I, withlin eclip)tie
limits, imore than thlree times. JIncnee, onlyl, three eclilpses cat
occlur successively while the stln is icar a mnode. "As lie passes
botlh nodes in tre salme year, tlherc may therelofre be six eclipses.
But a scventth may possibly colle just Nwithinll m12 m ioullths,