What is the Autumnal Equinox? - Earth.com
What is Autumnal Equinox?

What is the Autumnal Equinox?

For astronomers, the day that the sun’s path and the Earth’s celestial equator intersect signifies the Autumnal Equinox. During the Equinox, the entire planet receives about 12 hours of sunlight and darkness over the 24 hour period. The name is derived from the Latin words ‘aequi’ (equal), and ‘nox’ (night).

The Autumn, or Fall Equinox occurs between September 21 and 24 in the Northern Hemisphere. The date varies slightly each year due to factors such as the precession of the Equinoxes, the Earth’s axial precession, and the cycle of leap years in the Gregorian Calendar. In the Southern Hemisphere, the Spring Equinox occurs around the same date, marking the beginning of Spring.

How To Recognize the Equinox

  • During the Equinox, the sun rises directly in the east and sets directly in the west. 
  • The position of the sun at 12:00 noon changes day by day. Following the sun’s path throughout the year at it’s high point reveals what astronomers call the analemma — an augmented figure-8 shape. The Equinox occurs when the sun is at the center point of the anelemma.
  • Leading up to the day of the Equinox, the sun rises and sets increasingly to the north (in relation to the Equator), and afterwards, rises and sets increasingly to the south. 

Cultural Equinox Celebrations

The start of the Fall season is when the Neopagan Sabbat of Mabon is celebrated. Also, Autumnal Equinox Day is an official national holiday in Japan, and is spent visiting family graves, and holding family reunions. Some civilizations also celebrate the Harvest Moon, which is the full moon closest to the Autumn Equinox.

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