Science of The Spring: What is the Vernal Equinox?

SCIENCE OF THE SPRING

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In Colorado, we have a saying:

“We begin the first day of Spring like we began the Fall: with snow.”

This symmetry is relevant because the beginnings of Spring and Fall coincide with the Equinox.

This word consists of two Latin root words, aequus and nox, meaning “equal night,” referring to the fact that daylight and nighttime are equal in duration.

Equal Day and Night?

Almost. There’s actually more daylight than night on the day of an Equinox for two reasons. Our atmosphere bends (refracts) sunlight upward. Also, the Sun isn’t a single point of light but a large disk that’s very far away, about 92M miles away.

These factors increase the amount of daylight at the Equinox. The actual date of sunlight equality is 3 or 4 days ahead of the Equinox. But let’s keep this between us; we don’t want to spoil it for everyone else.

Date of Spring

This year, the vernal Equinox (Spring) occurs on March 20 at 09:02 UTC. This means Temps Universel Coordonne, or Coordinated Universal Time, if you don’t speak French, roughly equivalent to Greenwich Mean Time if you’re British, or Zulu Time if you’re a pilot. In the U.S., that’s 10:45 AM Eastern Time on March 20.

From Wikipedia:

UTC is based on TAI (International Atomic Time, abbreviated TAI, from its French name “temps atomique international”), which is a weighted average of hundreds of atomic clocks worldwide. UTC is within about one second of mean solar time at 0° longitude, the currently used prime meridian, and is not adjusted for daylight saving time.

Daylight Saving Time, that was so two weeks ago.

The Autumnal Equinox occurs six months later. Since each Equinox occurs simultaneously, whether in the northern or southern hemisphere – though the seasons are reversed – it is common to call the (northern) vernal Equinox the March Equinox and the Autumnal Equinox the September Equinox.

Vernal Equinox?

Where do we get the name vernal? It was St. Vernal of Bithynia in the 5th century who… No, just kidding. Vernal is from the Latin vernālis, from vernus, “of spring.”

It refers to the fresh or young part of the year. Remember, the ancient Romans (and Babylonians before them) started the year in March. At the moment of the Vernal Equinox, the Sun crosses the celestial equator — an imaginary line in the sky above Earth’s equator – from south to north.

In 2007, the Equinox occurred on March 21, as it did for most of the 20th century, but those days are gone. Now, the event slides earlier and earlier during the 400-year Gregorian calendar cycle. Now, the 21st century won’t show the Equinox until the 22nd century.

Faster Sunrise and Sunset

Sunset on the ocean. Image: Wikimedia

The sunsets and sunrises occur at their fastest on or near the Equinoxes. This phenomenon can be measured by determining the time it takes for the Sun’s entire disk to descend below the horizon. This is because the Sun sets at its steepest possible angle during the equinoxes.

This is also the week when the Sun’s rays reach their peak annual variation, providing an additional three minutes of daily sunshine in typical U.S. cities. Conversely, residents of Fairbanks, Alaska, experience nearly seven extra minutes of sunshine per day during this period.

Is it Getting Warmer?

On the Equinox, the Sun’s position relative to the zenith (direct overhead point) is always offset by the same number of degrees as the latitude. For example, in Bennington, Vermont, at a latitude of 43°, the midday Sun is 43° from precisely overhead on the equinox day. Consequently, it appears halfway up the sky.

This phenomenon represents a significant change from just a month ago and a dramatic shift since December, when the noon Sun rose only a mere one-fifth of the way up the sky. As solar rays exhibit greater intensity at higher elevations, such as my current location at 6,500 feet, the Sun’s growing intensity is palpable.

Furthermore, if you observe the sky at 1:00 PM each day, you’ll see that the Sun manages to climb four of its own diameters higher each week. This rapidly ratchets up its intensity. This is the year’s greatest solar energy boost for those who live north of the equator.

East and West

Earth lighting at the Equinox. Image: Wikimedia

On the Equinox, every place on Earth rotates perpendicularly into our planet’s “terminator”— its day-night shadow line. This is why on the Equinox, the Sun rises exactly in the east and sets exactly in the west. On other days, it’s “due east” and “due west.”

Ancient and pre-Christian cultures tracked the Sun’s movement for the Equinox and Solstice with markers, standing stones, standing circles, or monuments. Examples:

• Stonehenge, England
• Newgrange, Ireland
• Ring of Brodgar and Ballochroy, Scotland
• Carnac Stones, France
• Piedras Blancas, Spain
• Angkor Wat, Cambodia
• The Great Sphinx and Pyramid of Khafre, Egypt
• Machu Picchu, Peru
• Chichén Itzá, Mexico
• Chaco Canyon, New Mexico
• Casa Grande Ruins National Monument, Arizona
• Bighorn Medicine Wheel, Wyoming

East or West: Temples vs. Churches

I’ve written previously on the religious associations connected with Equinoxes and Solstices – of which there are four, two of each – and now we’re discussing the four points on the compass.

Speaking of Eastern orientation, most ancient temple entrances faced the East toward the sunrise. For pre-Christian temples, this was meant to welcome the rebirth of their god associated with the Sun.

The Jewish Temple of Solomon, later rebuilt as the Temple of Herod in Jerusalem, faced the East; worshipers had their backs toward the rising Sun. After the Temple was destroyed in 70 A.D., and into the 2nd century and beyond, Jewish synagogue entrances faced toward Jerusalem.

In the Hebrew Bible, Ezekiel 43-44 portrays God’s glory returning the same way it left – from the Mount of Olives to enter Jerusalem and the Temple from the East.

The New Testament, in Acts 1:11, says, “This Jesus, who was taken up from you into heaven, will come in the same way as you saw him go into heaven.” So also, from Matthew 24:27:

“For as the lightning comes from the east and shines as far as the west, so will be the coming of the Son of Man”

In Christian times, church and cathedral entrances usually faced the West. The first Byzantine church buildings (after A.D. 327) faced the West. Especially in Medieval times, the point of main interest in the interior of a church is towards the East (Latin: oriens). The east end is where the altar is placed, and the façade and main entrance are accordingly at the West end.

Temple of Hephaestus, Athens. Image: Wikipedia

When churches repurposed ancient “pagan” temples, they moved the entrance from the East to face the West. An example of this is my visit to the Agora in Athens, where, around A.D. 700, the Temple of Hephaestus (Roman: Vulcan) was converted into a Christian church dedicated to St. George. The temple originally had its entrance to the East, but when it became a church, the entrance was relocated to the West.

St. Stephen’s Cathedral, Vienna. Image: Wikipedia

In some cases, especially in later Medieval Europe, a church might be oriented to sunrise on the feast day of its patron saint. An example of this is St. Stephen’s Cathedral in Vienna, which is oriented to align with sunrise on St. Stephen’s Day, December 26, in the Julian calendar, 1137, when its construction began.

Relevance of Spring

As surely as Winter follows Autumn, so does Spring follow Winter

… except in Colorado, where I write this article. In most other parts of the U.S., we see the blossoming of new life. Many of this season’s holidays, both pagan and religious, point to new life.

In Gaelic or Celtic tradition, Imbolc marks the beginning of this season. Christians celebrate St. Brigid’s Day to mark the start of Spring, even though it usually falls in February. This points to the anticipation of the birth of Spring lambs, though in the U.S., it typically points to Groundhog Day.

Beltane usually ends this season in the Celtic calendar, known popularly as May Day. In the Christian calendar, Easter is the high point of the Spring festivals, celebrating “new life” through the resurrection of Jesus.

Spring has sprung
The grass has ris
I wonder where
The flowers is?

Colorado Springs Vinca (periwinkle), after a recent snowstorm. Author’s photo

Bill Petro, your friendly neighborhood historian
billpetro.com

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