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 Harvest Moon, this year the Full
Moon of September, occurs early Monday evening. Fall or Autumn begins
less than two days later on Wednesday afternoon.
Harvest Moon
For the year 2021, the Harvest Moon
will be the Full Moon of Monday Evening, September 20, at 7:54 p.m.
Eastern Daylight Saving Time (EDT) / 23:54 Coordinated Universal
Time (UTC). For farmers eager to finish harvesting their crops, the
bright Full Moon which shines on their farms for the several
evenings closest to the Autumnal Equinox (the Autumnal
Equinox is the astronomical beginning of the season of Autumn or Fall
in Earth's Northern Hemisphere) is called the Harvest Moon.
The
Harvest Moon is one of the signature astronomical events near the
beginning of, or shortly after the beginning of, the Fall season. It
is an event particularly anticipated by farmers of both the past and
the present. As many crops reach the time of harvest in late Summer
and early Autumn, often the work of the harvest has to continue past
sunset, which comes earlier and earlier each evening.
Nature has
come to the rescue of these farmers, with a bright Full Moon
(weather-permitting), which arrives just around the time of sunset,
that allows farmers and their staff to continue the harvest after the
Sun's light has dissipated. Hence, long-ago this Full Moon came to be
known as the Harvest Moon.
For a similar reason, the Full Moon of
October is often known as the Hunter's Moon, which allowed Native
Americans to continue the hunt after sunset, to begin to store meat
for the coming Winter months. However, the Harvest Moon is designated
as the closest Full Moon to the Autumnal Equinox, and such a Full
Moon does not always occur in September. Every few years the Harvest
Moon occurs in October, shortly after the Autumnal Equinox. During
those years, the Hunter's Moon occurs in November.
On average,
the Moon rises about 50 minutes later each day. However, during the
days near the Autumnal Equinox, the Moon rises each day only about
25-to-35 minutes later each day in the U.S.A., and only 10-to-20
minutes later in much of Canada and Europe. Thus, for several days
around the time of the Autumnal Equinox, the Harvest Moon appears to
rise around the same time each evening (roughly coinciding with local
sunset), providing light at the time most needed by farmers.
The
reason for this is due to the ecliptic, the apparent path of the Sun,
Moon, and planets through Earth's sky, which makes a narrow angle
with the horizon this time of year. It is this narrow angle which
provides that moonrise occurs around the time of sunset, near the
time of the Full Moon of September (or sometimes October). Hence,
several days appear to have a rising Full Moon.
Also, at this time
of year when farmers need moonlight the most, the Harvest Moon
appears larger and more prominent, due to the mysterious but
well-known "Moon Illusion" that makes the Moon seem larger
when it is near the horizon. And, while near the horizon, the Moon is
often reddened by clouds and dust, creating the appearance of a
large, rising red ball.
Some even liken a rising Harvest Moon
to a rising "Great Pumpkin," of Peanuts comic-strip
fame! In the Peanuts' network-television cartoon just before
Halloween each year (originally aired on CBS-TV on 1966 October 27) titled, "Its the Great Pumpkin, Charlie Brown",
the “Great Pumpkin” rises over the pumpkin patch to provide gifts
to all good little boys and girls.
In China and Vietnam, 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.
Native Americans
also called the Full Moon of September the Corn Moon or Barley Moon, as Corn and Barley were among their main crops. Sometimes, the September Full Moon in the
Northern Hemisphere is also known as the Fruit Moon.
In the
Southern Hemisphere, where Winter is about to turn to Spring, the
September Full Moon is known as the Worm Moon, Crow Moon, Sugar Moon,
Chaste Moon, or Sap Moon.
The Harvest Moon in the Southern Hemisphere
occurs in March or April, with the same advantages to Southern
Hemisphere farmers as the Harvest Moon in the Northern Hemisphere.
Beginning of Autumn
The
Autumnal Equinox (also known as the September Equinox), the beginning
of the season of Autumn or Fall in the Northern Hemisphere of Earth,
occurs Wednesday Afternoon, 2021 September 22 at 3:21 p.m. Eastern
Daylight Saving Time (EDT) / 19:21 Coordinated Universal Time (UTC).
In Earth's Southern Hemisphere, this equinox 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 [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 even bristles) on an Equinox, it can do
so any day of the year!
September 22 is also designated as the
annual Falls Prevention Awareness Day for this year.
Internet Links to Additional Information ---
Harvest Moon: Link >>> https://science.nasa.gov/science-news/science-at-nasa/2013/16sep_harvestmoon/
Native American Full Moon Names: Link >>> https://earthsky.org/astronomy-essentials/full-moon-names/
Mid-Autumn Festival / Moon Festival: Link >>> https://en.wikipedia.org/wiki/Mid-Autumn_Festival
Autumnal Equinox: Link >>>
http://scienceworld.wolfram.com/astronomy/AutumnalEquinox.html
Season of Autumn or Fall: Link >>>
http://en.wikipedia.org/wiki/Autumn
Equinox:
Link >>> http://en.wikipedia.org/wiki/Equinox
Equilux: Link
>>> https://darkskydiary.wordpress.com/2010/03/20/equinox-equilux-and-twilight-times/
Earth's Seasons: Link >>>
http://en.wikipedia.org/wiki/Season
Tilt
of a planet's axis: Link >>>
http://en.wikipedia.org/wiki/Axial_tilt
Urban
legend of eggs and brooms standing on their own, only on an
Equinox:
Link >>> http://www.snopes.com/science/equinox.asp
Falls Prevention Awareness Day: Link
>>> https://nationaltoday.com/falls-prevention-awareness-day/
Source:
Glenn A. Walsh Reporting for SpaceWatchtower,
a project of Friends
of the Zeiss.
Monday, 2021 September 20.
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gaw
Glenn A. Walsh, Informal Science Educator &
Communicator:
Link >>> http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/
Electronic
Mail: < gawalsh@planetarium.cc >
Project
Director, Friends of the Zeiss: Link >>> http://buhlplanetarium.tripod.com/fotz/
SpaceWatchtower
Editor / Author: Link >>> http://spacewatchtower.blogspot.com/
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 >>> http://www.planetarium.cc Buhl Observatory: Link >>> http://spacewatchtower.blogspot.com/2016/11/75th-anniversary-americas-5th-public.html
*
Adler Planetarium, Chicago: Link >>> http://adlerplanetarium.tripod.com
*
Astronomer, Educator, Optician John A. Brashear: Link >>> http://johnbrashear.tripod.com
*
Andrew Carnegie & Carnegie Libraries: Link >>> http://www.andrewcarnegie.cc
* Other Walsh Authored Blog &
Web-Sites: Link >>>
https://buhlplanetarium.tripod.com/gawweb.html
Latter phases of the Partial Lunar Eclipse / Partial Eclipse of the Moon seen from Gloucestershire, United Kingdom on 2019 July 17. A Partial Lunar Eclipse / Partial Eclipse of the Moon will be visible, weather-permitting, early on Friday Morning, 2021 November 19. November 19 also happens to be the 80th anniversary of the Astronomical Observatory 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).
Narrow Angle Camera image of the planet Neptune taken by the NASA Voyager 2 spacecraft on 1989 August 20, as the spacecraft approached the planet for an August 25 fly-by, the first and only visit to Neptune by a human-produced space probe. "The Great Dark Spot" and cirrus clouds are seen in the center. "Dark Spot, Jr." is seen rotating into view at the lower left of the disk, with a patch of cirrus clouds (called "Scooter") visible just north of Dark Spot, Jr.