This year’s first day of spring, or the spring equinox arrives on March 20 at 5:24 p.m. EDT. This day is also known as the vernal equinox.
Before I regale you with some pretty cool things about the spring equinox, we will get the science out of the way. Equinox comes from the Latin words “aequus” (equal) and “nox” (night).
Equinoxes are astronomical events that occur twice a year, with daylight and darkness being about the same length in both the Southern and Northern Hemispheres.
The astronomical definition uses the dates of equinoxes and solstices to mark the beginning and end of the seasons:
- Spring begins on the spring equinox;
- Summer begins on the summer solstice;
- Fall (autumn) begins on the fall equinox; and
- Winter begins on the winter solstice.
The Earth orbits the sun, at a tilt of about 23.5 degrees. This means that different parts of our planet receive more or less of the sun’s radiation at various times of the year, depending on our planet’s position in its orbit.
For every country on Earth, the sun rises in the east and sets in the west. However, the sun also appears to move north for half of the year and south for the other half, depending on where you are.
But twice a year — in March and September — our planet’s tilt aligns with its orbit around the sun, and Earth does not appear to tilt with respect to the sun, according to the National Oceanic and Atmospheric Association (NOAA).
A view of the eastern hemisphere showing noon in Central European time zone (ignoring DST) on the day of the equinox. Image credit – Przemyslaw “Blueshade” Idzkiewicz, CC SA 2.0.
At these special times of the year, the sun sits directly above the equator and both hemispheres get the same hours of daylight and night. The line that divides night and day, called the terminator, “grey line” or “twilight zone,” bisects the Earth and runs through the North and South poles.
You can impress your friends and family by pointing out that climate scientists use a different calendar to define the seasons — known as the “meteorological calendar.” The seasons are divided into four parts, with three months in each season.
Climate scientists base their calendar on the temperature cycle rather than the astronomical position of the sun — it’s easier to calculate statistics and forecast trends using full months and the same dates each year.
Some celebrations associated with the vernal equinox
As you can already guess, calendar dates play a significant role in our quest to define the seasons, and history shows us that any number of ancient civilizations revered the day of the vernal equinox as the time of new life returning to the Earth.
People have been tracking the sun’s movements for thousands of years, often incorporating equinoxes into cultural and religious traditions. For many ancient civilizations, these solar changes not only dictated the beginning of seasons but also when to plant and harvest crops.
For centuries, practitioners of Shintoism used the solar event as an occasion to honor their forebears. The Japanese government later converted this tradition into a secular, national holiday formally known as Vernal Equinox Day in the year 1948. It’s still being observed today.
Most Christian denominations celebrate Easter based on the date of the vernal equinox,. Easter occurs on the Sunday after the first full moon that follows March 21. What’s so special about this date? Well, it marks the so-called ecclesiastical Spring Equinox. Actually, Easter can fall as early as March 22 or as late as April 25.
For people of the Jewish faith, Passover usually falls on the first full moon after the northern hemisphere vernal equinox, although occasionally (currently three times every 19 years) it will occur on the second full moon.
“Navroz Mobarak!” The precise moment of the vernal equinox marks the first day of the first month on the Iranian solar calendar. It’s also the start of Nowruz, an awesome, 13-day celebration sometimes called the Persian New Year.
Observed by 300 million people around the world (mainly in central and western Asia), Nowruz is preceded by a flurry of household chores. After the spring cleaning ends, families enjoy decadent meals and sometimes paint eggs that represent fertility.
