equinox
EE-kwi-noks
/ˈiː.kwɪ.nɒks/
Either of the two moments in the year when the sun crosses the celestial equator, resulting in day and night being of equal length across the world.
Occurs twice annually—the vernal (spring) equinox in March and the autumnal equinox in September.
The story behind the word. Roman scholars observed that twice a year, night duration precisely matched day duration everywhere on Earth. They combined 'aequus' (equal) and 'nox' (night) to name these calendar markers 'aequinoctium'. Middle English adopted the term via Old French in the late fourteenth century.
Commonly confused with
- solstice: Equinox means equal night (12h day / 12h night), whereas solstice marks maximum daylight or night duration.
Word family
- equinoctial (adjective): Pertaining to an equinox or occurring at the time of an equinox.
Collocations
- vernal equinox
- autumnal equinox
- spring equinox
- march equinox
Example sentences
- "During the autumnal equinox, day and night are of virtually equal length across every continent on the globe." Astronomy overview
- "Mayan architects constructed the pyramid at Chichen Itza so that shadow snakes appear during the vernal equinox." Archaeology
Memory hook
EQUI-NOX = EQUAL NIGHT (and day). EQUINOX = Equal Night across the planet.
When not to use
Do not confuse with solstice, which represents the longest or shortest day rather than equal hours.
Fun facts
- On the exact day of an equinox, the sun rises due east and sets due west everywhere on Earth except at the geographic poles.
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