CHAP. I.
THEORY OF ECLIPSES.
85
to pass over the other extreme body, as it enters upon orleaves the common line of direction. The phenomena result-ing from such contingencies of position and direction arevariously denominated ‘ Eclipses' ‘ Transits' and ‘ Occult a-tions' according to the relative apparent magnitudes of theinterposing and obscured bodies, and according to the cir-cumstances which attend them.” We shall proceed to considerthe several phenomena in detail, beginning with Eclipses.
It must be premised, that the Moon ’s orbit does not lie inexactly the same plane as the Earth ’s, but is inclined theretoat an angle of about 5 0 8' 48”. The two points where its
Fig. 16.
path intersects the ecliptic are called the nodes , and the ima-ginary line joining these points is termed the line of nodes.When the Moon is crossing the ecliptic from south to north,it is passing its ascending node (Sb); the opposite point of
Fig. 17.
its orbit being the descending node (IS). If the Moon shouldhappen to pass through either node at or near the time ofconjunction, or New Moon , it will necessarily come betweenthe Earth and the Sun , and the 3 bodies will be in the samestraight line; it will therefore follow that, to certain partsof the Earth , the Sun ’s disc will be obscured, wholly or par-tially as the case may be : this is an Eclipse of the Sun . Inthe figures above, S, represents the Sun , E, the Earth , andM, the Moon .