86

THE MOON .

diagram the portion of the Moon ’s orbit which is clotted issnpposed to be slightly below the plane of the Earth ’s path(or the ecliptic), and the other portion slightly above it.

If, then, upon one of the days upon which such a passageoccurs, the Moon is full, as in the positions N, and m 2 in the abovefigure, a total eclipse of the longest possible duration will beseen, the Moon passing through the very centre of the Earth ’sshadow, as in Fig. XXI.

It is also found that if the Moon on such a day is within abouteleven days before or after being Full, an eclipse of some kind,either partial or total, but of shorter duration, will take place

Earths Shadow

Fig. XXII.—Showing how the Moon , when full, may escape being eclipsed.

at the next following, or next preceding, Full Moon , when theMoon will still pass within so small a distance, above or belowthe straight line joining the centres of the Earth and of theSun , that it will in some degree traverse the umbra of theEarth’s shadow. At all other times the Full Moon will, inconsequence of the tilt, or inclination, of its orbit to the planeof the ecliptic, in which the Earth circles round the Sun , passaltogether above or below the Earth ’s umbra, and escapeeclipse, and it will pass clear of the shadow by the greatestpossible distance when it occupies such positions as m 3 and m 4in Fig. XX., which correspond to places of the Earth justhalf-way between those which coincide with the occurrenceof the longest possible eclipses. We have endeavoured toillustrate such an escape from eclipse in Fig . XXII.