History of Fall: What is the Autumnal Equinox?

Equinox. Author’s iPhone photo

HISTORY OF THE FALL: What is the Autumnal Equinox?

Podcast

This time of year corresponded to New Year’s Day in the French Republican Calendar. However, since that calendar was only in use from 1793 to 1805, following the abolishment 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, which is associated with the Equinox. This word is composed of two Latin roots, aequus and nox, meaning “equal night,” referring to the fact that daylight and nighttime are of equal duration. Americans call the season Fall, from “fall of the leaf,” while Brits say Autumn, a later French and Latin import.

What happens during the Equinox?

Astronomical

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 22, at 8:05 pm EDT, which is September 23 at 00:05 UTC, which is temps universel coordonné (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.

Historical Trivia:

The abbreviation “UTC” is a compromise: when the ITU standardized the term around 1970, English wanted CUT and French wanted TUC, so they settled on neither.

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 refer to the (northern) vernal equinox as the March Equinox and the Autumnal Equinox as 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 at about 6 PM local time, depending on the time zone, in most places on the planet except the poles
• In other words, daytime and nighttime are roughly worldwide, not counting atmospheric refraction
• 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
• Equinoxes are the only times when both the North and South Poles are lit by sunlight at the same instant

Fall

Welcome September. Image generated by DALL-E 3

Meteorologically, Fall begins September 1. Meteorologists break down the year into three-month seasons based on annual temperature cycles. By that calendar, Spring starts on March 1, Summer on June 1, Fall on September 1, and Winter on December 1.

However, over the years, due to a confluence of influences, owing to 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.”

The end of Summer vacation is no longer observed following the Labor Day holiday.

Bill Petro, your friendly neighborhood historian
billpetro.com

Podcast: