To illustrate this, let ABCD be the Ecliptic, RSTU a Circle lying in the same Plane with the Ecliptic, and VWXY the Moon’s Orbit, all thrown into an oblique view, which gives them an elliptical shape to the eye. One half of the Moon’s Orbit, as VWX, is always below the Ecliptic, and the other half XYV above it. The points V and X, where the Moon’s Orbit intersects the Circle RSTU, which lies even with the Ecliptic, are the Moon’s Nodes; and a right line as XEV drawn from one to the other, through the Earth’s center, is the Line of the Nodes, which is carried almost parallel to itself round the Sun in a year.
If the Moon moved round the Earth in the Orbit RSTU, which is coincident with the Plane of the Ecliptic, her shadow would fall upon the Earth every time she is in conjunction with the Sun; and at every opposition she would go through the Earth’s shadow. Were this the case, the Sun would be eclipsed at every Change, and the Moon at every Full, as already mentioned.
But although the Moon’s shadow N must fall upon the Earth at a, when the Earth is at E, and the Moon in conjunction with the Sun at i, because she is then very near one of her Nodes; and at her opposition n she must go through the Earth’s shadow I, because she is then near the other Node; yet, in the time that she goes round the Earth to her next Change, according to the order of the letters XYVW, the Earth advances from E to e, according to the order of the letters EFGH, and the line of the Nodes VEX being carried nearly parallel to itself, brings the point f of the Moon’s Orbit in conjunction with the Sun at that next Change; and then the Moon being at f is too high above the Ecliptic to cast her shadow on the Earth: and as the Earth is still moving forward, the Moon at her next opposition will be at g, too far below the Ecliptic to go through any part of the Earth’s shadow; for by that time the point g will be at a considerable distance from the Earth as seen from the Sun.
Fig. I and II.
When the Earth comes to F, the Moon in conjunction with the Sun Z is not at k, in a Plane coincident with the Ecliptic, but above it at Y in the highest part of her Orbit: and then the point b of her shadow O goes far above the Earth (as in Fig. II, which is an edge view of Fig. I.) The Moon at her next opposition is not at o (Fig I) but at W where the Earth’s shadow goes far above her, (as in Fig. II.) In both these cases the line of the Nodes VFX (Fig. I.) is about 90 degrees from the Sun, and both Luminaries as far as possible from the limits of Eclipses.
When the Earth has gone half round the Ecliptic from E to G, the line of the Nodes VGX is nearly, if not exactly, directed towards the Sun at Z; and then the New Moon l casts her shadow P on the Earth G; and the Full Moon p goes through the Earth’s shadow L; which brings on Eclipses again, as when the Earth was at E.
When the Earth comes to H the New Moon falls not at m in a plane coincident with the Ecliptic CD, but at W in her Orbit below it: and then her shadow Q (see Fig. II) goes far below the Earth. At the next Full she is not at q (Fig. I) but at Y in her orbit 51⁄3 degrees above q, and at her greatest height above the Ecliptic CD; being then as far as possible, at any opposition, from the Earth’s shadow M (as in Fig. II.)
So, when the Earth is at E and G, the Moon is about her Nodes at New and Full; and in her greatest North and South Declination, (or Latitude as it is generally called) from the Ecliptic at her Quarters: but when the Earth is at F or H, the Moon is in her greatest North and South Declination from the Ecliptic at New and Full, and in the Nodes about her Quarters.
The Moon’s ascending and descending Node.
Her North and South Latitude.