This diagram shows the position of the Earth, in relation to the Sun,
at the time of the Vernal Equinox at the official beginning of the
season of Spring in the Earth's Northern Hemisphere (Autumn in Earth's
Southern Hemisphere), 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
Spring begins early Saturday morning at
the moment of the Vernal Equinox in Earth's Northern Hemisphere. In
the Southern Hemisphere of Earth, this marks the astronomical
beginning of the season of Autumn.
Vernal Equinox on Earth
The Vernal Equinox occurs on Earth at
precisely: 5:37 a.m. Eastern Daylight Saving Time (EDT) / 9:37
Coordinated Universal Time (UTC) on Saturday Morning, 2021 March 20.
As the diagram at the beginning of this
blog-post demonstrates, on the day of 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 a 23.439281-degree
angle from the plane of the Earth's orbit around the Sun, which is
part of the Ecliptic of our Solar System. 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 a half-year
later during that hemisphere's season of Winter. As mentioned, during
an Equinox (about half-way between Summer and Winter, and about
half-way between Winter and Summer) 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.
March 16 marked 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 and 3-to-4 days
after the Autumnal Equinox (Equilux is on September 25, while the
Autumnal Equinox is ~ September 22 or 23).
An urban legend that has been making
the rounds for decades, now exacerbated by the Internet and Social
Media, 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 and
stiff bristles) on an Equinox, it can do so any day of the year!
In ancient times, the Vernal Equinox
was considered the beginning of the new calendar year, as Spring
brought new life after the cold Winter months. The calendar year was
then defined as the time from one Vernal Equinox to the next. This is
known as the Tropical Year: 365 days, 5 hours, 48 minutes, and 45
seconds.
This was when most of Western
Civilization used the Julian Calendar, recommended by astronomer
Sisogenes and approved by Roman leader Julius Caesar in 46 B.C. Due
to the difference between the Julian Calendar and the calendar we use
today, known as the Gregorian Calendar, the Vernal Equinox then
occurred on March 25, later observed by Christians as the Feast of
the Annunciation (observed nine full months before Christmas Day). As
part of the Gregorian Calendar reform, in October of 1582, Roman
Catholic Pope Gregory XIII chose the Feast of the Circumcision of
Christ (January 1) as the beginning of the New Year in the Roman
Catholic Church's Liturgical Year.
The Vernal Equinox continues to be
considered the beginning of the New Year, or an important holy day,
in several other places on Earth ---
* Beginning of New Year (using the
Solar Calendar) - Nowruz: Afghanistan and Iran / Persia.
* Holy Day for adherents of the
Zoroastrian Religion (the three Magi, who the Christian Bible reports
visited the Christ Child after following the Star of Bethlehem /
Christmas Star, were adherents of the Zoroastrian Religion).
* Holy Day for adherents of the Bahá'Ã
Faith: Baha'i Naw-Ruz, one of nine holy days of the Bahá'à Faith.
NASA and the European Space Agency
(ESA) observe Sun-Earth Day on or near the Vernal Equinox. This is a
joint educational program started in 2000, to popularize the
knowledge about the Sun, and the way it influences life on Earth,
among students and the public. This is part of Solar Week, which is
the calendar week that includes the Vernal Equinox.
The first week of Spring, beginning
with the Vernal Equinox, has been declared by physicians as Medicine
Cabinet Clean-Up Week. To avoid prescription drug abuse, particularly
important at this time of the opioid crisis, physicians encourage
everyone to get rid of unused and no-longer-needed medications and
other drugs, which may have lingered in the household, as part of an
annual Spring cleaning. Several states have prescription drug
take-back locations, where these drugs can be dropped-off.
The week of the Vernal Equinox is the
also the beginning of the National Cherry Blossom Festival held each
year in Washington, DC, which begins on March 20. This festival
commemorates the 1912 gift of 3,000 cherry trees from the Mayor of
Tokyo to the City of Washington. The festival runs through April 11
this year and will be available both on-line and with events in
Washington, according to the National Cherry Blossom Festival web-site: “with an innovative format that honors the tradition of
the Festival, while prioritizing the health and safety of
participants amidst the coronavirus pandemic.”
Internet Links to Additional Information ---
Vernal
Equinox: Link >>> https://en.wikipedia.org/wiki/March_equinox
Season
of Spring: Link >>>
http://en.wikipedia.org/wiki/Spring_%28season%29
Equinox:
Link >>> http://en.wikipedia.org/wiki/Equinox
Earth's
Seasons: Link >>> http://en.wikipedia.org/wiki/Season
Tilt
of a Planet's Axis: Link >>>
http://en.wikipedia.org/wiki/Axial_tilt
Related Blog-Post ---
"Mon.: Winter Begins & Great Conjunction: Jupiter & Saturn; Tue: Ursid Meteors." Sun., 2020 Dec. 20.
Source:
Glenn A. Walsh Reporting for SpaceWatchtower,
a project of Friends
of the Zeiss.
Saturday, 2021 March 20.
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Glenn A. Walsh, Informal Science Educator &
Communicator:
Link >>> http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/
Electronic
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Project
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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
*
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*
Andrew Carnegie & Carnegie Libraries: Link >>> http://www.andrewcarnegie.cc
Expected landing site on Mars for NASA's Perseverance Rover, including the Ingenuity Helicopter Drone. Landing sites of some previous NASA missions to Mars are also shown.