Equinox
astronomical event where the Sun is directly above the Earth's equator
A solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun rises almost exactly in the east and sets almost exactly in the west. This occurs twice each year, around 20 March and 23 September.
An equinox is defined as the time when the plane of Earth's equator passes through the geometric center of the Sun's disk. This is also the moment when Earth's rotation axis is perpendicular to the Sun-Earth line, tilting neither toward nor away from the Sun. Because the Moon and (to a lesser extent) the planets cause Earth's orbit to vary slightly from a perfect ellipse, the equinox is officially defined by the Sun's more regular ecliptic longitude rather than by its declination. The instants of the equinoxes are currently defined to be when the apparent geocentric longitude of the Sun is 0° and 180°.
The word is derived from the Latin aequinoctium, from aequa (equal) and nox (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. Contrary to popular belief, they are not exactly equal, due to the angular size of the Sun, atmospheric refraction, and the changing duration of the length of day that occurs at most latitudes around the equinoxes.
Begin with the source’s own compact description: “Equinox” is astronomical event where the Sun is directly above the Earth's equator. The dossier treats that line as a proposition to test through Equinox, astronomical and event, not as a finished interpretation.
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Chronology, provenance and viewpoint should be read together before a broad social or political interpretation is accepted. The source revision retrieved here is dated Sep 23, 2026. The linked authority identifier is Q1315. None of the 0 selected statements returned an explicit reference.
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This entry incorporates text from “Equinox” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.