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

160'rutn, ~itoN,.
reckonedl fro the first, in consequence of the batckard motion of tihe tnodes.
270. It hars been observed already, that were the spectator
oni tie mloon insteadc of on lhe earth, he wouild see the earth
eclipsed by tile mloon, and the calculation of the eclipse \ould
be very sinmillar to that of a lunar eclipse; but to an observer
on tile earth the eclipse does not of corlse begin lwhIen the
eartll irst. enters tile moonl's shadow, andi it is necessary to determine not only \ Iwhat portion of the earth's surfiace will be
covere(d by thle oon's shadow, but like1wise the patlh described
by its cente'r relative to various places oil the surface of tlle
earth. Thlis is known whIlen the latitude and longitude of tlhe
center of' the shadow oin tile earth is determined for each
instalnt. T'l'e latitude and longitqide, of the moon are, found oil
the s)upplosition that the spectator views it from the center of
thte arthl, wheretas hlis position on the surfitce changes, in consequence of parallax, botl tlhe latitude an8d lonlitude and the
amlount of these changes must ble accurately estimated, before
the appearancea of tll eclipse at any partictldar place can ble
fitlly d(termniled.
Tlhlec details of thle method of calculating a solar eclipse can
ntot be unders'tood in any way so wcell as 1by actually performingo thle lrocess according to a given exasmple. For suchf
details, theretbre, thle reader is referred to thle t'qpki2lment.
271. In total eclipses tire has sometimes been seen at
remarkablW radiation of lighlt around tle moon, while the suni
is bellind it.'i'llis is called a coiroa, and al)l)ears to be concentric withl tle slln's disk, ratller tllan with tile Illollo's. It is
by solme considered to indicate the existence of an extensive
solar atLlospllere.
Anotlher ilnterestint g phenomenon often attends the momtent of
concealmnent andl real)learanc of the sun's edge fat the begillning and end of total darkness, as also thfe formnation and rupture of thle ringt in alnular eclipses. it is the d(ividing up of
theo fiine tlllread of the su's edge into a series of bright beads.
Becinl first noticcd by Mr.:'.41rancis Baily, they are known by
tlhe name of Atily's.1eal. T Ile al)ppearalnce is tby some attributed to the light of tihe sutns elge comling through b)etween