The Fall Equinox Isn't On September 21st? ©

 

Autumn in Minister Valley, Pennsylvania; photo by Kathleen Reynolds

In “How to Find Your Way Without A Compass, Part One, Orientation By The Sun” (HERE), which I wrote earlier this year, and in “Part Three, The Shadow-tip Method” (HERE); I wrote that in 2019, the Fall Equinox will be on September 23^rd.  Since I published these articles, I have received several questions regarding the 23^rd as the date of the upcoming equinox.  

 

Most people wondered if I had mistyped the date, since accepted, common knowledge is that the Fall Equinox is on September 21^st, the Spring Equinox is on the 21^st of March, the Winter Solstice is on December 21^st and finally the Summer Solstice is on the 21^st of June.  Unfortunately in this case, common knowledge is only mostly right and the various equinoxes and solstices occur, either one or two days before or after the 21^st, and for the most part, very rarely on the 21^st.

But why is that, you ask, or at least that is what I asked myself, and so maybe you asked it too.  I didn’t know the answers, so I did some research, because that is what I do; and here are the “whys” and the “whens” of our yearly equinoxes and solstices.

Everyone knows, that on the coming Fall, or as it is more correctly known, September Equinox¹ the Sun rises exactly in the east and sets directly over the west.  But what causes an equinox and why is it on September 23^rd, in 2019, and not on the 21^st?

Earth’s Axial Tilt from “The September Equinox”, by www.timeanddate.com

Equinox is from the Latin, “aequinoctium”, meaning “equal night” and there are two equinoxes every year, one in September and one in March.  On these two days, the length of day and night is nearly equal at roughly 12 hours each, all over the world, and that is why they are called equinoxes.  Also, on both of them the sun rises in the east directly over the Equator and sets directly over the Equator in the west; because on these days the tilt of the Earth’s axis is perpendicular to the Sun’s rays.  The equinox occurs the moment the sun crosses the Earth’s celestial equator, the imaginary plane in the sky that extends directly out from the Earth’s equator and the exact date and time of this occurrence varies from year to year.  The March Equinox is both the beginning of spring in the Northern Hemisphere and the beginning of fall in the Southern Hemisphere and the September Equinox, which in the Northern Hemisphere is the beginning of fall, is also the beginning of spring in the Southern Hemisphere.

Most often the September Equinox falls on either the 22^nd or the 23^rd. Less often the September Equinox is on the 21^st or the 24^th; the last time it was on the 21^st was in the year 1000 and the next time it will fall on that day is in 2092.  Also, the last time the September Equinox fell on the 24^th was in the year 1931 and the next time will be in 2303.

The same pattern occurs with the March Equinox, which happens most often on the 20^th, and less often on the 19^th.

Solstice is from the Latin “solstitium” and it means “sun-stopping”.  There are also two solstices every year, and depending on which hemisphere you are in and they are both the shortest and the longest days of the year.  In the Northern Hemisphere, the June Solstice is the longest day of the year and the start of summer; while in the Southern Hemisphere it is the shortest day of the year and the beginning of winter.  Six months later, on the December Solstice, everything is reversed and it is the shortest day of the year in the Northern Hemisphere and the start of winter and it is the longest day of the year and the start of summer in the Southern Hemisphere.  Solstices occur when the Sun’s zenith is at its farthest point from the equator.  On the June Solstice, the Sun reaches its farthest point north at 23.4^o north latitude; the North Pole tilts towards the Sun and the Sun is visible all night from just south of the Arctic Circle to the North Pole; and the Sun rises to the north of east and sets to the north of west.  Also, south of the Antarctic Circle, there is no sunlight at all on the June Solstice.  On the December Solstice, the Sun reaches its most southern point at 23.4^o south latitude; the South Pole tilts towards the Sun and from just north of the Antarctic Circle to the South Pole the sun remains visible all night; and the Sun rises to the south of east and sets to the south of west.  From approximately the Arctic Circle to the North Pole, the sun remains below the horizon all day and there is no sunlight at all.

Most often the June Solstice occurs on the 21^st and only slightly less often it occurs on the 20^th.  Similarly the December Solstice, at least for the next 30 years, happens only on the 21^st.  So, in the case of the yearly solstices, common knowledge is mostly correct.

In the end though, common knowledge is close enough because as Richard Graves noted when he wrote about equinoxes on page 330 of, The 10 Bushcraft Books, “…for about two or three weeks either side of the Equinoctial periods…on any day between March 1^st and April 14^th or September 1^st and October 14^th…” the Sun rises and sets close enough to the true east-west line to use the sunrise and sunset to orient yourself.  Similarly, for about two to three weeks on either side of the solstices the Sun will be close to either its northern or southern zenith.  So whether it is the 19^th or 24^th, 22^nd, 21^st or 23^rd; it doesn’t really matter when all is said and done.

I hope that you continue to enjoy The Woodsman’s Journal Online and my videos at BandanaMan Productions and don’t forget to follow me on both The Woodsman’s Journal Online and subscribe to BandanaMan Productions on YouTube, and if you have questions, as always, feel free to leave a comment on either site.  I announce new articles on Facebook at Eric Reynolds, on Instagram at bandanamanaproductions, and on VK at Eric Reynolds, so watch for me.

Notes

¹  I accidentally fell into a Northern Hemisphere-centric bias when I wrote my earlier articles in the “How To Find Your Way Without A Compass” series.  Seasons are opposite each other on either side of the Equator, and so using the descriptor, “Fall” for the coming equinox is both inaccurate and a bit of a misnomer, since the equinox that takes place in September is the Fall Equinox for the Northern Hemisphere and the Spring Equinox for the Southern Hemisphere.  Additionally, using “Spring” for the March Equinox and “Winter” and “Summer” for the December and June solstices is also incorrect.  My apologies to all of my readers, south of the Equator.

Sources

Grant, Megan; “Why Isn't The Fall Equinox On Sept. 21? The Earth's Axis & Rotation Around The Sun Are Incredibly Powerful”, September 21, 2016, https://www.bustle.com/articles/185268-why-isnt-the-fall-equinox-on-sept-21-the-earths-axis-rotation-around-the-sun

Graves, Richard; The 10 Bushcraft Books, [CreateSpace Independent Publishing Platform, Middletown, Delaware, USA, December 20, 2017]

  

“June Solstice: Longest and Shortest Day of the Year”, [Time and Date AS 1995–2019], https://www.timeanddate.com/calendar/june-solstice.html

“March Equinox - Equal Day and Night, Nearly”, [Time and Date AS 1995–2019], https://www.timeanddate.com/calendar/march-equinox.html

“Solstices & Equinoxes for Buffalo (2000—2049)”, [Time and Date AS 1995–2019], https://www.timeanddate.com/calendar/seasons.html?year=2000

“The September Equinox”, [Time and Date AS 1995–2019], https://www.timeanddate.com/calendar/september-equinox.html

“Winter Solstice – Shortest Day of the Year”, [Time and Date AS 1995–2019], https://www.timeanddate.com/calendar/winter-solstice.html