Autumnal Equinox, happened two times every year when the Sun is exactly above the Equator and day and night are of equal length; also, either of the two points in the sky where the ecliptic (the Sun’s annual pathway) and the celestial equator intersect.
In the Northern Hemisphere the autumnal equinox falls either on September 22 or 23, as the Sun crosses the celestial equator going south.
In the Southern Hemisphere the equinox also falls either on March 20 or 21, when the Sun moves north across the celestial equator.
The time varies based on area or time zone, but if you’re on Eastern Time, it happens this year at September 22, 2016 at 10:21am. However, no matter where you are in the world, the equinox means that day and night are almost exactly the same length, an almost perfect 12 hours apiece.
According to the astronomical definition of the seasons, the autumnal equinox also marks the beginning of the autumn season, which lasts until the winter solstice. A solstice is an astronomical event that occurs twice each year during the month of June and December as the Sun reaches its highest or lowest excursion relative to the celestial equator on the celestial sphere.
Source: britannica, bustle
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