NODES

, the two opposite points where the orbit of a planet intersects the ecliptic. That, where the planet ascends from the south to the north side of the ecliptic, is called the Ascending Node, or the Dragon's Head, and marked thus <*>: and the opposite point, where the planet descends from the north to the south side of the ecliptic, is called the Descending Node, or Dragon's Tail, and is thus marked <*>. Also the right line drawn from the one Node to the other, is called the Line of the Nodes.

By observation it appears that, in all the planets, the Line of the Nodes continually changes its place, its motion being in antecedentia; i. e. contrary to the order of the signs, or from east to west; with a peculiar degree of motion for each planet. Thus, by a retrograde motion, the line of the moon's nodes completes its circuit in 18 years and 225 days, in which time the Node returns again to the same point of the ecliptic. Newton has not only shewn, that this motion arises from the action of the sun, but, from its cause, he has with great skill calculated all the elements and varieties in this motion. See his Princip. lib. 3, prop. 30, 31, &c.

The moon must be in or near one of the Nodes to make an eclipse either of the sun or moon.