equinox

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The Word of the Day for September 22 is:

equinox   \EE-kwuh-nahks\   noun
     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

Example sentence: 
     During the equinox, day and night are approximately of 
equal length around the world.

Did you know? 
     "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.

*Indicates the sense illustrated in the example sentence.