| Term: | Equinox |
| Definition: |
One of the two points on the celestial sphere where the celestial equator intersects the ecliptic, that is when the apparent ecliptic longitude of the Sun is 0° or 180°. At equinox, the length of the day and the night are equal all over the globe. The equinox is not a fixed point; it moves due to precession and nutation. If only precession is considered, we deal with the mean equinox of date. If nutation is also taken into account, then we are concerned with the true equinox. |