Monday, September 19, 2022

Fall Begins at Equinox Thur. Evening
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 (a.k.a. Buhl Science Center - Pittsburgh's science and technology museum from 1939 to 1991) and Founder of the South Hills Backyard Astronomers amateur astronomy club; permission granted for only non-profit use with credit to author.) 

By Glenn A. Walsh

Reporting for SpaceWatchtower

The Autumnal Equinox on Thursday evening 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 beginning of the season of Autumn or Fall in Earth's Northern Hemisphere of Earth, occurs Thursday Evening, 2022 September 22 at 9:04 p.m. Eastern Daylight Saving Time (EDT) / September 23 at 1:04 Coordinated Universal Time (UTC). In the Southern Hemisphere, this moment marks the astronomical beginning of the season of Spring.

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.

September 25 will mark 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.

Although, Western Cultures consider September the beginning of 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 Mid-Autumn Festival was held on Saturday, 2022 September 10, coinciding with this year's Harvest Moon, the Full Moon of September.

September 22 is also designated as Falls Prevention Awareness Day for this year.

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 ---

"More Evening Light w/ Harvest Moon This Weekend." Tue., 2022 Sept. 6.

Link >>>

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

               Monday, 2022 September 19.

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Glenn A. Walsh, Informal Science Educator & Communicator                                                               (For more than 50 years! - Since Monday Morning, 1972 June 12):
Link >>>
Electronic Mail: < >
Project Director, Friends of the Zeiss: Link >>>
SpaceWatchtower Editor / Author: Link >>>
Formerly Astronomical Observatory Coordinator & Planetarium Lecturer, original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center), Pittsburgh's science & technology museum from 1939 to 1991.
Formerly Trustee, Andrew Carnegie Free Library and Music Hall, Pittsburgh suburb of Carnegie, Pennsylvania.
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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