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| 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 23rd. Since I published these articles, I have
received several questions regarding the 23rd 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 21st, the Spring
Equinox is on the 21st of March, the Winter Solstice is on December
21st and finally the Summer Solstice is on the 21st 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 21st, and for the most
part, very rarely on the 21st.
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 23rd, in 2019, and not on the 21st?
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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 22nd or the 23rd.
Less often the September Equinox is on the 21st or the 24th;
the last time it was on the 21st 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 24th
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 20th,
and less often on the 19th.
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 23.4o 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 23.4o 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 21st and only slightly less
often it occurs on the 20th.
Similarly the December Solstice, at least for the next 30 years, happens
only on the 21st. 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 1st and
April 14th or September 1st and October 14th…”
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 19th or 24th,
22nd, 21st or 23rd; 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
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