Monday, September 18, 2023

Fall Begins at Equinox This-Coming Weekend

This diagram shows the position of the Earth, in relation to the Sun, at the time of the Autumnal Equinox, as well as the other equinox and solstices of the year.

[Graphic Source: ©1999, Eric G. Canali, former Floor Operations Manager of the original Buhl Planetarium and Institute of Popular Science / Buhl Science Center (America's 5th major planetarium & Pittsburgh's science and technology museum from 1939 to 1991) and Founder of the South Hills Backyard Astronomers amateur astronomy club. Permission granted for non-profit use only, with credit to author.]

By Glenn A. Walsh

Reporting for SpaceWatchtower

The Autumnal Equinox early Saturday morning marks the end of the season of Summer and the beginning of Fall or Autumn in Earth's Northern Hemisphere. In the Southern Hemisphere, this marks the transition from Winter to Spring.

The Autumnal Equinox (also known as the September Equinox), the end of Summer and the beginning of the season of Autumn or Fall in Earth's Northern Hemisphere, occurs Saturday Morning, 2023 September 23 at 2:50 a.m. Eastern Daylight Saving Time (EDT) / 6:50 Coordinated Universal Time (UTC). In the Southern Hemisphere, this moment marks the astronomical beginning of the season of Spring.

Autumn or Fall continues in the Northern Hemisphere, and Spring in the Southern Hemisphere, until the December Solstice: Thursday Evening, 2023 December 21 at 10:27 p.m. Eastern Standard Time (EST) / December 22 at 3:27 UTC. At the moment of the December Solstice, Winter begins in the Northern Hemisphere and Summer begins in the Southern Hemisphere.

The approximate and traditional mid-way point between the Autumnal Equinox and the Winter Solstice comes in the vicinity of October 31 (All-Hallows Eve or Halloween) / November 1 (All-Saints Day) / November 2 (All-Souls Day): the Astronomical Cross-Quarter Day of Samhain or All-Hallowsmas. The actual November Cross-Quarter Day will be Tuesday Morning, 2023 November 7 at 11:18 a.m. EST / 16:18 UTC. The one-week discrepancy between the October 31 and November 7 dates is due to the fact that the traditional date of Samhain was fixed on October 31, when the Julian Calendar was still in use.

In ancient times, a calendar season was considered the time between one Cross-Quarter Day and the next Cross-Quarter Day. So, Autumn was considered the time between August 1 (Lughnasadh or Lammas Day), which was the traditional beginning of the wheat harvest, to October 31 (Samhain). Samhain actually means “Summer's end” as the Celtic calendar only considered two main seasons: Summer and Winter.

The Celtic peoples of Ireland began celebrations on Samhain in the 5th century B.C. Samhain was considered by the Celtics and Druids on the British Isles as the end of the old year, with the following day the beginning of the New Year. In A.D, 835, the Roman Catholic Church named November 1 All-Saints Day with the previous day becoming All-Hallows Eve or Halloween, the eve or evening before All-Saints Day.

It is believed that in ancient times the Pleiades Star Cluster, also known as the Seven Sisters, culminated (climbed to the cluster's highest point in the sky) around Midnight local time on or near Samhain. Samhain and Pleiades Culmination would have occurred together around A.D. 11th and 12th centuries before the Gregorian Calendar was instituted. For the Pleiades Culmination to occur during the dark time of the year's end, many peoples felt this was a time to honor the dead. Although today Pleiades Culmination occurs on November 21, the Pleiades still can be seen high in the sky around local Midnight on Halloween, weather-permitting.

On the day of the Equinox, the Sun appears directly overhead at local Noon on the Equator. At the moment of Equinox, the Northern and Southern Hemispheres of Earth are illuminated equally. And, the time of Equinox is the only time when the Earth Terminator (dividing line on Earth between daylight and darkness) is perpendicular to the Equator.

This, and the reason for seasons on Earth in the first place, is due to the fact that Earth rotates on its axis, which is tilted at an approximate 23.44-degree angle from the Ecliptic, the plane of the Earth's orbit around the Sun. As the Earth revolves around the Sun, this axial tilt causes one hemisphere of the planet to receive more direct solar radiation during that hemisphere's season of Summer and much less direct solar radiation about a half-year later during that hemisphere's season of Winter. As mentioned, during an Equinox [in the Northern Hemisphere: about half-way between Summer and Winter (Autumnal Equinox), and about half-way between Winter and Summer (Vernal Equinox)] both planetary hemispheres receive an equal amount of solar radiation. 

Although "Equinox" in Latin means equal-night, the day of the Equinox does not actually have an equal amount of daylight and nightfall, as it appears on the Earth's surface. If the Sun was just a pin-point of light in our sky, as all other stars appear, day and night would be equal.

But, because the Sun is a disk, part of the Sun has risen above the horizon before the center of the Sun (which would be the pin-point of light); so there are extra moments of light on the Equinox. Likewise, part of the Sun is still visible, after the center of the Sun has set.

Additionally, the refraction of sunlight by our atmosphere causes sunlight to appear above the horizon, before sunrise and after sunset.

Each year, September 25 or 26 (Sept. 26 in 2023) marks the Equilux ("equal-light"), the actual day with equal hours and minutes of the Sun above the horizon, and equal hours and minutes of the Sun below the horizon. The Equilux occurs twice each year, approximately 3-to-4 days before the Vernal Equinox, when Spring begins,  and 3-to-4 days after the Autumnal Equinox, after Autumn or Fall has begun.

An urban legend that has been making the rounds for decades has it that eggs can be stood on their ends only during an Equinox, whether the Vernal Equinox in the Spring or the Autumnal Equinox in the Fall. This is completely false. Depending greatly on the size and shape of the particular egg, eggs can be stood on their ends any day of the year! Astronomy has nothing to do with whether an egg can stand on its end. If an egg can stand on its end on the Equinox (and, due to the shape and size of some eggs, this is not even possible), it can stand the same way any other day of the year.

In the last few years, with the help of the Internet and Social Media, another urban legend has become prevalent. Now it is claimed that brooms can stand, on their own, on their bristles, only on an Equinox day. This is also false. Again, as with eggs, if a broom can stand on its bristles by itself (this usually only works with newer brooms, with more stiff and even bristles) on an Equinox, it can do so any day of the year!

In China, Vietnam, Korea, Japan, and other nations in East and Southeast Asia, a popular harvest festival is celebrated on the date close to the Autumnal Equinox of the Solar Cycle, as well as close to the Harvest Moon. This Mid-Autumn Festival / Moon Festival dates back more than 3,000 years to Moon worship in China's Shang Dynasty.

Again, as Western Cultures consider September the beginning of Autumn (meteorologists and climatologists consider September 1 the beginning of Meteorological Autumn), the ancients often termed this as "Mid-Autumn". By this reckoning, Autumn actually began at the traditional Cross-Quarter Day of August 1 (when some harvesting actually begins) and ends at the traditional Cross-Quarter Day of All-Hallow's Eve, also known as Halloween.

On the Chinese Han Calendar, the Mid-Autumn Festival falls on the 15th day of the 8th month (on a day between September 8 and October 7 in our Gregorian Calendar). This usually falls on the night of a Full Moon, the Harvest Moon. This year, the Harvest Moon occurs on Friday Morning, 2023 September 29 at 5:57 a.m. EDT / 9:57 UTC.

September 22 is designated as Falls Prevention Awareness Day.

Internet Links to Additional Information ---

Mid-Autumn Festival / Moon Festival: Link >>>

Cross-Quarter Day: Link >>>

Autumnal Equinox: Link >>>

Season of Autumn or Fall: Link >>>

Equinox: Link >>>

Equilux: Link >>>

Earth's Seasons: Link >>>

Tilt of a planet's axis: Link >>>

Urban legend of eggs and brooms standing on their own, only on an Equinox:
Link >>>

Falls Prevention Awareness Day: Link >>>

Related Blog-Post ---

"Summer Begins Mid-Day Wednesday at Solstice." Mon., 2023 June 19.

Link >>>

Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss          

               Monday, 2023 September 18.

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Glenn A. Walsh, Informal Science Educator & Communicator                                                               (For more than 50 years! - Since Monday Morning, 1972 June 12):
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Formerly Astronomical Observatory Coordinator & Planetarium Lecturer, original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center), America's fifth major planetarium and Pittsburgh's science & technology museum from 1939 to 1991.
Formerly Trustee, Andrew Carnegie Free Library and Music Hall, Pittsburgh suburb of Carnegie, Pennsylvania, the fourth of only five libraries where both construction and endowment funded by famous industrialist & philanthropist Andrew Carnegie.
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh: Link >>>  Buhl Observatory: Link >>>
* Adler Planetarium, Chicago: Link >>>
* Astronomer, Educator, Optician John A. Brashear: Link >>>
* Andrew Carnegie & Carnegie Libraries: Link >>>

 * Other Walsh-Authored Blog & Web-Sites: Link >>>

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