# equinox

/ˈikwəˌnɑks/ (US) · /ˈɛkwɪnˌɒks/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/equinox
Updated: 2026-05-11

## Definition

one of the two days in the year when day and night are exactly the same length. This happens in March and September when the sun is directly over the equator.

For teachers: the moment when the sun crosses the celestial equator, resulting in a day and night of approximately equal duration globally. Occurs twice annually, around March 20 and September 23.

## Examples

- The spring equinox marks the first day of spring.
- Ancient civilizations often built stone monuments aligned with the sun's position during the autumn equinox.
- During the equinox, the Earth's axis is tilted neither toward nor away from the sun, creating a brief period of symmetry in the distribution of light across both hemispheres.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.