equinox

/ˈikwɪnɑks/

/ˈikwɪnɒks/

Other forms: equinoxes

The equinox is one of the two times in a year when the sun crosses the plane of the earth's equator, and day and night are of equal length. “During the spring equinox you can balance eggs on end, because of the equal balance between night and day.”

There are two equinoxes every year, one in the spring (the vernal equinox) and one in the fall (the autumnal equinox), each usually on the first day of spring and the first day of fall. These days are often celebrated and even worshipped in some traditions, although an equinox is actually a point in time — not an entire day.

Definitions of equinox

1. noun

   either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length
   types:

   March equinox

   a time when the Sun's path crosses northward over the equator, marking the start of spring in the northern hemisphere and of fall in the southern hemisphere

   autumnal equinox, fall equinox

   September 22

   Noruz, Nowrooz, Nowruz

   (Persian) the new year holiday in Iran and Azerbaijan and Afghanistan and Pakistan and parts of India and among the Kurds; comes at the vernal equinox

   type of:

   cosmic time

   the time covered by the physical formation and development of the universe
2. noun

   (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic
   synonyms: equinoctial point

   types:

   vernal equinox

   (astronomy) the point in the sky, currently in the constellation of Pisces, where the Sun's apparent path crosses Earth's equator from south to north

   autumnal equinox

   (astronomy) the equinoctial point that lies in the constellation of Virgo

   type of:

   celestial point

   a point in the heavens (on the celestial sphere)