Word of the Day:

1 : either of the two points on the celestial sphere where the celestial equator intersects the ecliptic

2 : either of the two times each year (as about March 21 and September 23) when the sun crosses  the equator and day and night are everywhere on earth of approximately equal length

Though many in the U.S. and Canada consider summer to end on Labor Day, the autumnal equinox, which falls on September 22nd or 23rd (and the latter in 2015), marks the true beginning of autumn.

"In between the solstices are the equinoxes, when the Sun reaches its midpoint in the sky and the day has an equal amount of daylight and darkness." — Kevin Schindler, The Arizona Daily Sun, 1 Aug. 2015

More example sentences

Equinox descends from aequus, the Latin word for "equal," and nox, the Latin word for "night"—a fitting history for a word that describes days of the year when the daytime and nighttime are equal in length. In the northern hemisphere, the vernal equinox marks the first day of spring and occurs when the sun moves north across the equator. (Vernal comes from the Latin word ver, meaning "spring.") The autumnal equinox marks the first day of autumn in the northern hemisphere and occurs when the sun crosses the equator going south. In contrast, a solstice is either of the two moments in the year when the sun's apparent path is farthest north or south from the equator.