History of Fall: What is the Autumnal Equinox?


This time of year represented New Year’s Day, according to the French Republican Calendar. However, since that calendar was only in use from 1793 to 1805, following the fall of the French monarchy in 1792, very few still celebrate this day.


Date of Autumn

Instead, September 22 or 23 marks the beginning of Fall or Autumn associated with the Equinox. This word is made up of two Latin root words aequus and nox meaning “equal night” referring to the fact that daylight and nighttime are equal in duration.


Astronomical Fall

When the plane of the earth’s equator passes through the center of the Sun, metaphorically speaking, you have evennight, twice a year. This year, the astronomical autumnal equinox (Fall) occurs on September 23 at 01:04 UTC. This means Temps Universel Coordonne (or Coordinated Universal Time) if you speak French, roughly equivalent to Greenwich Mean Time if you’re British, Zulu Time if you’re a pilot. The Vernal Equinox occurs six months later.

Since each equinox occurs at the same time whether in the northern hemisphere or the southern hemisphere, though the seasons are reversed, it is becoming common to call the (northern) vernal equinox the March Equinox and the Autumnal Equinox the September Equinox, thereby avoiding that annoying Northern Hemisphere bias.

During the Equinox:

  • The Sun rises due east and sets due west
  • The Sun rises at about 6 AM and sets about 6 PM local time in most places on the planet except the poles
  • In other words, daytime and nighttime are about the same length, worldwide
  • The center of the visible Sun is exactly above the Equator
  • The edge between night and day (solar terminator) is perpendicular to the Equator, equally illuminating both the northern and southern hemispheres.


Meteorological Fall

Meteorologically, Fall begins September 1. But over the years due to a confluence of influences including in part truancy, sunspot activity, cosmic ray interference, and standardized testing, many students now return to classrooms in August — completely ruining the song “See You In September” — and currently the end of Summer vacation is no longer observed following the Labor Day holiday.


Bill Petro, your friendly neighborhood historian


If you enjoyed this article, please consider leaving a comment.
Subscribe to have future articles delivered to your email.

About billpetro

Bill Petro has been a technology sales enablement executive with extensive experience in Cloud Computing, Automation, Data Center, Information Storage, Big Data/Analytics, Mobile, and Social technologies.

Leave a Comment