This diagram shows the position of the Earth, in relation to the Sun, at the time of the Vernal Equinox, the official beginning of the Season of Spring, as well as the other solstices and equinox of the year.
(Graphic Source: ©1999, Eric G. Canali, former Floor Manager of Pittsburgh's original Buhl Planetarium and Institute of Popular Science 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 Vernal Equinox, which marks the
beginning of the Season of Spring in Earth's Northern Hemisphere, occurs
for 2017 on Monday Morning, March 20 at 6:29 a.m. Eastern Daylight
Saving Time (EDT) / 10:29 Coordinated Universal Time (UTC).
In the Southern Hemisphere, this marks the astronomical beginning of the Season of Autumn.
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 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 degrees, 26 minutes, 13.4 seconds (23.43705 degrees) angle from 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 a half-year later during that hemisphere's Season of Winter. As mentioned, during an Equinox [about half-way between Summer and Winter (for Autumn or Fall), and about half-way between Winter and Summer (for Spring)] both planetary hemispheres receive an equal amount of solar radiation.
In the Southern Hemisphere, this marks the astronomical beginning of the Season of Autumn.
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 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 degrees, 26 minutes, 13.4 seconds (23.43705 degrees) angle from 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 a half-year later during that hemisphere's Season of Winter. As mentioned, during an Equinox [about half-way between Summer and Winter (for Autumn or Fall), and about half-way between Winter and Summer (for Spring)] both planetary hemispheres receive an equal amount of solar radiation.
In Latin, Equinox, is defined as
equal-night, the day when daylight and darkness are about
equal in length. Such actual equal-night never occurs on the
actual date of an Equinox on Earth. This is due to the fact that the
Sun is so large, in relation to the Earth, and hence, the entire Sun
does not appear at actual sunrise, only a portion of the Sun; it
takes a few more minutes for the entire Sun to appear above the
horizon. Also, due to the refractive nature of Earth's
atmosphere, daylight can be seen before the Sun's disk can be
observed.
The date of actual equal-night
varies by a location's longitude and latitude. At the Earth's
Equator, daytime is always longer than night. Hence, the Equator
never has equal-night.
While the Vernal Equinox, the true
beginning of the Season of Spring, occurs on March 20 at 6:29 a.m.
EDT / 10:29 UTC, the literal Equinox for Spring, termed
the Spring Equilux,
actually occurs each year a few days earlier, usually around March
16 or 17 (depending on the specific location).
The Vernal Equinox is used in the solar
calendars of Iran and Afghanistan as the beginning of their calendar
year. In ancient times, the Vernal Equinox, then celebrated by the
old style calendar on or near March 25, was also the beginning of the
calendar year for many ancient civilizations.
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!
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!
This year, the Primary Moon Phase of
Last Quarter for March occurs just a few hours after the Vernal
Equinox: March 20 at 11:58 a.m. EDT / 15:58 UTC.
There is now an effort to have the
day of the Vernal Equinox designated to commemorate the life of the
first female astronomer, Hypatia of Alexandria, in ancient Egypt: Hypatia Day / Women in Science Day.
Astronomical historian Ari
Belenkiy, who finished an academic paper in 2016 on the life and death
of Hypatia, has started an effort to have the day of the Vernal
Equinox, March 20, designated by the Canadian Parliament as a day
commemorating Hypatia's life. According to Professor Belenkiy,
Hypatia's last days were dedicated to finding the exact time of the
Vernal Equinox.
Hypatia was a
Greek astronomer, mathematician, and philosopher, daughter of the
mathematician Theon Alexandricus, who lived in Alexandria, Egypt
during the late 4th and early 5th centuries. At
that time Alexandria was part of the Eastern Roman Empire, which had
a great rivalry with the Church of Rome. This led to deep divisions
in Alexandria.
Due to the fog of
time, there is much dispute regarding the events surrounding the
death of Hypatia. According to the Church historian Socrates
Scholasticus, a clique of Bishop Cyril's zealots killed Hypatia, due
to a deep conflict between the Governor and Bishop of Alexandria.
Hypatia's astronomical calculations regarding the date of Easter may
have set the mob against her.
Although none of Hypatia's writings survive, she is reported to have made significant academic contributions in the fields of Astronomy and Mathematics.
The beginning of Spring also marks the
beginning of the National Cherry Blossom Festival held each year in
Washington, DC. This festival commemorates the 1912 gift of 3,000
cherry trees from the Mayor of Tokyo to the City of Washington. This
year, the festival runs from March 15 through April 16.
Physicians have declared the first week
of Spring as Medicine Cabinet Clean-Up Week. They urge families, as
part of their annual Spring cleaning, to clean-out the medicine
cabinet of old and expired pharmaceuticals which are no longer being
used. This would prevent other family members from using these old
drugs by accident, or the beginning of drug abuse.
Internet Links to Additional Information ---
Vernal Equinox: Link >>> http://scienceworld.wolfram.com/astronomy/VernalEquinox.html
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
Hypatia:
Link 1 >>> https://en.wikipedia.org/wiki/Hypatia
Link 2 >>> http://booksandjournals.brillonline.com/content/journals/10.1163/15700720-12341264
Petition to designate March 20 to commemorate the life of Hypatia:
Link >>> https://www.change.org/p/canada-s-parliament-commemorating-the-first-female-astronomer-hypatia-of-alexandria
National Cherry Blossom Festival, Washington:
Link >>> http://www.nationalcherryblossomfestival.org/?id=404
Medicine Cabinet Clean-Up Week: Link >>> http://www.prnewswire.com/news-releases/include-medicine-cabinets-on-your-spring-cleaning-list-300042760.html
Special Thanks: Eric G. Canali, former Floor Manager of Pittsburgh's original Buhl Planetarium and Institute of Popular Science and Founder of the South Hills Backyard Astronomers amateur astronomy club.
Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss.
2017 March 19.
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Glenn A. Walsh, Project Director, Friends of the Zeiss: < http://buhlplanetarium.tripod.com/fotz/ >
& SpaceWatchtower Editor / Author: < http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/ >
Electronic Mail - < gawalsh@planetarium.cc >
Astronomy Links: < http://buhlplanetarium.tripod.com/#astrolinks >
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South Hills Backyard Astronomers Blog: < http://shbastronomers.blogspot.com/ >
Barnestormin Blog: Writing, Essays, Pgh. News, etc.: < http://www.barnestormin.blogspot.com/ >
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh:
< http://www.planetarium.
* Adler Planetarium, Chicago:
< http://adlerplanetarium.
* Astronomer, Educator, Optician John A. Brashear:
< http://johnbrashear.tripod.com >
* Andrew Carnegie & Carnegie Libraries:
< http://www.andrewcarnegie.
* Civil War Museum of Andrew Carnegie Free Library:
< http://garespypost.tripod.com >
* Duquesne Incline cable-car railway, Pittsburgh:
< http://inclinedplane.tripod.
* Public Transit:
< http://andrewcarnegie2.tripod.
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