Emily Dickinson Lexicon

E-QUI-NOC'TIAL, n. [for equinoctial line.]

In astronomy, a great circle of the sphere, under which the equator moves in its diurnal course. This should not be confounded with the equator, as there is a difference between them; the equator being movable, and the equinoctial immovable; the equator being drawn about the convex surface of the sphere, and the equinoctial on the concave surface of the magnus orbis. These words, however, are often confounded. When the sun, in its course through the ecliptic, comes to this circle, it makes equal days and nights in all parts of the globe. The equinoctial then, is the circle which the sun describes, or appears to describe, at the time the days and nights are of equal length, viz. about the 21st of March and 23d of September. Encyc. Equinoctial points, are the two points wherein the equator and ecliptic intersect each other; the one, being in the first point of Aries, is called the vernal point or equinox; the other, in the first point of Libra, the autumnal point or equinox. Encyc. Equinoctial dial, is that whose plane lies parallel to the equinoctial. Encyc. Equinoctial time, is reckoned from a fixed instant common to all the world.