What Is The Spring Equinox? A Guide To One Of The Most Significant Events In The 2025 Astronomical Calendar

4th Jan 2025

Spring represents the blossoming of the new, freshness, renewal, and hope. It is as if nature gets its second wind and wakes up after hibernation, giving all living things on Earth a long-awaited thaw. For us, this magical time traditionally begins on 1st March, but according to the astronomical calendar, the beginning of spring is considered to be the vernal equinox day. Let’s dive into the world of astronomy and find out what is the spring equinox and what makes it so special.

What Is The Spring Equinox?

earth and flower — Move over, winter: It’s time for the spring equinox. Credit: Janet Loehrke/USA TODAY

Spring or vernal equinox is the moment when the centre of the Sun crosses the celestial equator, moving from the Southern Hemisphere to the Northern Hemisphere. The celestial equator is an imaginary projection of the Earth’s equator onto the celestial sphere.

What happens during the spring equinox? The Earth’s axis and orbit align so that both hemispheres receive an equal amount of sunlight. This makes day and night approximately equal in length, which gives the phenomenon its name (from the Latin words “aequus” — equal and “nox” — night).

The vernal equinox marks the beginning of astronomical spring in the Northern Hemisphere and autumn in the Southern Hemisphere, symbolising balance and harmony in nature. After this day, the nights in the Northern Hemisphere become shorter and the daylight hours longer, signalling the arrival of true spring.

Equinox comes not only in spring but also in autumn. Then, everything happens the other way around. The sun crosses the celestial equator, moving from North to South. In the Northern Hemisphere, astronomical autumn begins, and in the Southern Hemisphere, spring.

When Is The Spring Equinox In 2025 And Why Does Its Date Change?

vernal equinox meaning — The vernal equinox time around the world. Credit: wgntv.com

Spring equinox typically occurs on 19, 20, or 21 March in the Northern Hemisphere and 21-24 September in the Southern Hemisphere. Dates vary for several reasons.

The Difference Between Calendar And Astronomical Year

The Earth orbits the Sun in about 365.24 days. However, our calendar year is 365 days long. To compensate for this quarter-day difference and to even out the equinox dates, people invented leap years, adding an extra day to February every four years. Without leap years, equinox dates would gradually shift backwards, as they did under the Julian calendar.

Precession Of The Earth’s Axis

Precession is a slow change in the direction of the Earth’s rotation axis caused by the gravitational pull of the Moon and the Sun. Precession causes equinox dots to shift across the celestial sphere, causing the phenomenon to occur slightly earlier each year compared to the year before. This shift is approximately 20 minutes and 24 seconds per year. A full precession cycle, during which the equinox dots return to their original positions, takes about 25,800 years.

Earth’s orbit

The Earth’s orbit around the Sun is not a perfect circle but an ellipse. This means that the distance between the Earth and the Sun changes throughout the year. The Earth is closer to the Sun at perihelion (early January) and further from the Sun at aphelion (early July). At perihelion, the Earth moves faster because the Sun’s gravitational pull is stronger. At aphelion, our star’s gravity is weaker, and the Earth moves more slowly. The constant change in the Earth’s orbital speed also affects the dates of the September and March equinox.

Astronomers have calculated that, in the 21st century, the equinox most often occurs on March 20 (78 times) and September 22 (76 times). On March 19, the event will occur 20 times, but only twice on March 21. But the next equinox on September 24 will occur only in 2303! But keep in mind that the above dates are given in GMT, so they may differ in other time zones.

What Day Is The Spring Equinox 2024/2025?

In 2024, the vernal equinox in the Northern Hemisphere occurred on March 20 at 03:06 UTC. In the Southern Hemisphere, the event occurs on September 22. The centre of the Sun will cross the celestial equator at 12:44 UTC.

In 2025, astronomical spring in the Northern Hemisphere will begin on March 20 at 09:02 UTC and in the Southern Hemisphere — on September 23 at 06:20 UTC.

When Is The Spring Solstice In 2025?

Solstices and equinoxes phases — Solstices and equinoxes. Credit:media.bom.gov.au

There is no such thing as a “spring solstice,” only a “vernal equinox.” But, sometimes, confusion can arise because both solstice and equinox characterise the length of day and night and occur twice a year. However, that’s where their similarities end.

The solstice occurs when the Earth’s axis is tilted toward or away from the Sun at its maximum angle; that is, the Sun is at its maximum or minimum deviation from the equator. This results in the longest (summer solstice) and shortest (winter solstice) days of the year. The summer solstice usually falls on June 20 or 21, and the winter solstice on December 21 or 22.

Thus, if day and night are almost equal in length during the equinox, then during the solstice, the day is either the longest or the shortest of the year.

How Is The Vernal Equinox Reflected In History And Culture?

The Temple of Kukulcan. Chichen Itza. Mexico. Credit: chichenitza7.com

The March equinox is not only an astronomical event but also an important cultural event that has been celebrated by people for thousands of years.

Maya

For the Maya, this event helped determine the time of planting and harvesting, as well as unite their society and strengthen their connection with the gods. One of the most famous places where the Maya celebrated the equinox is Chichén Itzá, an ancient city located on the Yucatan Peninsula in Mexico and recognised as one of the New Seven Wonders of the World. During these days, a unique phenomenon of light and shadow occurs on the Kukulkan pyramid. The sun’s rays create the illusion of a snake descending the pyramid steps. This snake symbolises the supreme Mayan god Kukulkan.

Celts

March equinox was known to the Celts as “Alban Eiler” or “Light of the Earth.” Various rituals using “Sop seile” or “wisp of straw” were performed on this day. For example, a purification ritual involved dipping a bundle of straw into water that had come into contact with silver or gold (such as wedding rings). This water was then sprinkled on the house and its inhabitants as protection against evil spirits and the evil eye. The Celts also used “sop seile” to bless horses, harnesses, and ploughs. This was made to ensure a fruitful agricultural season.

Germanic tribes

Germanic people celebrated Ostara (or Ēostre), a festival dedicated to the goddess of spring and dawn. Her name is associated with the rebirth of nature and fruitfulness. The festival marked the first day of spring and the beginning of the agricultural year. One of the main traditions on this day was the baking of small wheat buns and the dyeing of eggs, which symbolised new life. Ostara is still celebrated today, mainly by neo-pagan movements such as Wicca, Druids, and Asatru.

Persia and Central Asia

The people of Iran, Afghanistan, and Central Asia celebrate Nowruz, the Persian New Year. This holiday has an over 3,000-year-old history and symbolises the victory of light over darkness, renewal, and rebirth of nature. One of the key traditions of Nowruz is the preparation of the Haft-sin table, containing seven objects with names starting with the letter “s” in Persian. These objects represent different aspects of life, such as health, wealth, and love.

Nowruz is recognised by UNESCO as humanity’s intangible cultural heritage. It continues to play an important role in the cultural identity of people celebrating it.

Japan

In Japan, March equinox day is known as Shunbun no Hi and is a national holiday. On this day, Japanese people visit the graves of their ancestors, spend time with family, and go for walks to enjoy the sakura blossoms and other spring signs.

Shunbun no Hi has religious significance in both Buddhism and Shintoism. In Buddhism, this day is associated with the concept of “Higan” (彼岸), which means “distant shore” and symbolises the soul’s passage to the world of ancestors.

How Did The Ancients Determine The Equinox?

Ancient temples and pyramids were built exactly in line with the sun. Credit: Business insider

Today, September and March equinox dates are calculated by astronomers for decades in advance and are no secret to anyone. Modern instruments and calendars allow this to be done without much difficulty. But how did the ancients know when day and night become equal?

On an equinox day, the sun rises due east and sets due west. A compass helps determine which is east and which is west. The first compass was invented in China around the time of the Sòng Dynasty (960-1279 AD). How, then, did earlier civilisations manage to build their temples and pyramids so nearly perfectly aligned with the cardinal directions?

To do this, they used various objects, such as a gnomon or an astronomical ring. These objects were placed on a flat surface and cast shadows. During the period when the day was equal in length to the night, the shadows were minimal and uniform. As described by Ptolemy, who lived in the second century AD, to determine the equinox, he placed a flat bronze ring parallel to the equator. When the Sun was on one side of the equator, the corresponding side of the ring was illuminated. The transition moment was the moment of equinox.

Why The Equinox Is Not Exactly The Equinox: Debunking The Popular Myth

day and night are not equal on the equinox — Optical illusion created by the bending of sunlight through the atmosphere (known as refraction). This physical process provides an extra 8 to 12 minutes of sunlight through the Equinox. Credit: iweathernet.com

Despite common misconception, the duration of day and night in the equinox is not perfectly equal. The day is always longer by an average of 10 minutes! There are two reasons for this — sunset/sunrise definition and atmospheric refraction.

We know that on equinox day, the sun rises exactly in the East and sets exactly in the West. However, the sun is a disk, not a point. Sunrise is the moment when the upper edge of the solar disk rises above the horizon, and sunset is when the upper edge sets below the horizon. The time it takes for the horizon line to pass from edge to edge of the disk takes several minutes.

Now add refraction, the optical effect of the atmosphere refracting sunlight, to this. Think of a spoon in a glass of water. If you look at it from a certain angle, it seems to bend. In the same way, the Earth’s atmosphere refracts the sun’s rays and the apparent altitude of the sun increases by about 0.5 degrees when the sun is near the horizon. This means that when you see the edge of the setting Sun, it has already completely disappeared. Atmospheric refraction and the time it takes for the sun’s disk to completely cross the horizon make equinox light day an average of 10 minutes longer than night (depending on latitude).

The only exceptions are the poles, where there is no daily change of day and night. The polar night here is replaced by the polar day, and each last for 6 months.

However, there is a moment when the duration of day and night becomes equal. It is called equilux. On such a day, daylight lasts almost 12 hours (plus or minus a few tens of seconds). Equilux occurs a few days before and after September or March equinox, and its exact date depends on the latitude.

March Equinox 2025: The Gates Of Spring

The spring equinox is not just an astronomical event. Its rich cultural and practical heritage remains relevant to this day. It is a starting point for renewal, harmony and growth, because the increase in daylight hours has a positive effect on many areas of our life, such as agriculture, climatology and ecology, ethology, human health, etc. It is also an eternal symbol of hope, which we feel with a flutter every time we stand at the gates of spring.