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), America's fifth major planetarium and 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 Monday afternoon 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.
The Vernal Equinox occurs on Earth at precisely: 5:24 p.m. Eastern Daylight Saving Time (EDT) / 21:24 Coordinated Universal Time (UTC) on Monday, 2023 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.
"Vernal" is a Latin term for Spring. 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.
In addition to being St. Patrick's Day, today (2023 March 17) 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 (some years the Equilux occurs on March 16). 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 Sosigenes 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.
As a legacy to the Vernal Equinox originally considered the beginning of the New Year, astronomers have set the Vernal Equinox as the beginning point of the coordinate system in the sky. Astronomers measure the sky using Right Ascension (measured in hours, minutes, and seconds), which is analogous to Longitude on Earth, and Declination (measured in degrees, minutes, and seconds), which is analogous to Latitude on Earth. Precisely on the Vernal Equinox each year, the sky coordinates are reset to Right Ascension 0 hour, 0 minute, 0 second, and Declination 0 degree, 0 minute, 0 second.
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'í Faith: Baha'i Naw-Ruz, one of nine holy days of the Bahá'í 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.
March 20 is also considered Women in Science Day or Hypatia Day. Hypatia was an astronomer, mathematician, philosopher, and teacher in 5th century Alexandria, Egypt, then part of the Eastern Roman Empire. She was a prominent thinker in Alexandria whose murder (in March of A.D. 415) shocked the empire; she became a secular “martyr for philosophy”. The Vernal Equinox is considered a logical day to celebrate the life of Hypatia, as her last days were dedicated to finding the precise time of the Vernal Equinox, as a means to set the date of Easter.
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; some are located in pharmacies and / or municipal building lobbies.
The week of the Vernal Equinox is also the beginning of the National Cherry Blossom Festival held each year in Washington, DC, which begins on March 18. 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 16 this year. For 2023, the National Park Service predicts the Peak Bloom of the Cherry Blossoms will be March 22 to 25.
Almost a day after the Vernal Equinox comes March's Primary Lunar Phase of New Moon (Lunation #1240). The New Moon Phase occurs at 1:23 p.m. EDT / 17:23 UTC on Tuesday, 2023 March 21.
Sunday, 2023 March 19 at 11:00 a.m. EDT / 15:00 UTC marks the monthly Lunar Perigee (when the Moon is closest to the Earth for the month): 225,368.846 statute miles / 362,696 kilometers. At the same time is a conjunction, when the planet Saturn appears 4 degrees north of the Moon (you would need to look before Sunrise to see this conjunction, weather-permitting, when the Moon will be in a very slim, Waning Crescent Phase).
Internet Links to Additional Information ---
Vernal Equinox -
Link 2 >>> 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
Sun - Earth Day: Link >>> https://en.wikipedia.org/wiki/Sun-Earth_Day
Women in Science Day / Hypatia Day: Link >>> https://www.change.org/p/canada-s-parliament-commemorating-the-first-female-astronomer-hypatia-of-alexandria
Medicine Cabinet Clean-Up Week: Link >>> https://www.prnewswire.com/news-releases/include-medicine-cabinets-on-your-spring-cleaning-list-300042760.html
National Cherry Blossom Festival: Link >>> https://nationalcherryblossomfestival.org/
Related Blog-Post ---
"Daylight Saving Time Returns - Year-round?" Fri., 2023 March 10.
Friday, 2023 March 17.
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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 >>> 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