What happens on the autumnal equinox?

During the autumnal equinox in the Northern Hemisphere, the sun moves precisely above the equator, and the sun’s path and the celestial equator align while the sun heads South. 

When this happens, the length of night and day are exactly the same. The autumnal equinox falls about September 22 or 23, as the Sun crosses the celestial equator going south.

Further Readings-

1. Difference Between Summer and Winter Solstice
2. Motions of the Earth

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