The vernal equinox is the moment when the center of the Sun crosses directly above Earth’s equator, moving from the Southern Hemisphere into the Northern Hemisphere. It marks the astronomical start of spring in the north and autumn in the south, and it falls on March 20 in most years. In 2025, it occurs on March 20 at 9:01 UTC; in 2026, on March 20 at 14:46 UTC.
What Happens in Space
Earth’s axis is tilted about 23.5 degrees relative to its orbit around the Sun. For most of the year, that tilt means one hemisphere receives more direct sunlight than the other. Twice a year, the geometry lines up so that neither hemisphere is tilted toward or away from the Sun. Those two moments are the equinoxes.
At the vernal equinox, the Sun’s path across the sky (called the ecliptic) intersects the plane of Earth’s equator projected into space (the celestial equator). That intersection point is known in astronomy as “the first point of Aries” because it once sat in the constellation Aries. Due to a slow wobble in Earth’s axis called precession, that point has drifted. It moved into the constellation Pisces around the year 1 CE and is currently shifting toward Aquarius. The full cycle of this wobble takes roughly 26,000 years, a phenomenon first identified by the Greek astronomer Hipparchus around 130 BC.
Why Day and Night Aren’t Quite Equal
The word “equinox” comes from Latin for “equal night,” which suggests 12 hours of daylight and 12 hours of darkness. In reality, the day is slightly longer than the night on the equinox, for two reasons.
First, the Sun is a disk, not a point. Sunrise is defined as the moment the upper edge of the Sun peeks above the horizon, and sunset as the moment the upper edge disappears below it. That adds a few extra minutes of visible sunlight on each end of the day. Second, Earth’s atmosphere bends light. This refraction lifts the Sun’s image so you can see it several minutes before it has geometrically reached the horizon in the morning, and several minutes after it has dropped below it in the evening. Combined, these effects mean the equinox day is about 7 minutes longer than the night at latitudes up to 25 degrees, and 10 minutes or more longer at 50 degrees latitude.
The actual date when day and night are closest to equal length is called the “equilux,” and it falls a few days before the March equinox. The exact date depends on your latitude. In the UK in 2021, for example, the equilux fell on March 17, three days before the equinox.
Spring in the North, Autumn in the South
The term “vernal equinox” specifically refers to the start of spring, so it only applies to the Northern Hemisphere. South of the equator, the same astronomical event signals the beginning of autumn, with shorter days, earlier sunsets, and cooling temperatures ahead. To avoid confusion, many astronomers simply call it the “March equinox,” which is hemisphere-neutral. The September equinox plays the reverse role: spring in the south, autumn in the north.
Cultural Celebrations Tied to the Equinox
The vernal equinox has anchored holidays and rituals across cultures for thousands of years. Nowruz, the Persian New Year, begins on the first day of spring and is celebrated by hundreds of millions of people across Iran, Central Asia, and diaspora communities worldwide. Easter’s date is calculated from the equinox as well: it falls on the first Sunday after the first full moon following the vernal equinox, a formula established in the fourth century.
In Japan, the equinox is a national holiday called Shunbun-no-hi. Families visit the graves of relatives and pour water on headstones or into flower vases in a ceremony called Mizu-matsuri. Similar traditions of honoring ancestors around the equinox exist in Korea. In the Western pagan tradition, groups of modern druids gather at Stonehenge each March to watch the sunrise over the ancient stones, while crowds assemble at the foot of the Pyramid of the Sun in Teotihuacán, Mexico.
Ancient Monuments Built for the Equinox
Some of the world’s oldest structures were deliberately aligned to capture equinox sunlight. The Great Sphinx of Giza faces due east and stares directly into the rising Sun on the equinoxes. At a 4,000-year-old Egyptian monument, sunlight travels down an east-west hallway to illuminate specific statues. A 5,000-year-old underground Celtic temple channels the rising Sun through a long shaft to light an engraved wall.
The most famous equinox spectacle may be at Chichén Itzá in Mexico. The pyramid known as El Castillo was designed so that on the equinoxes, late-afternoon sunlight creates a pattern of triangular shadows along its staircase. The shadows connect with a carved serpent head at the base, making it look as though the snake god Kukulkán is slithering down the side of the temple. Equinox alignments have also been documented at Stonehenge, Machu Picchu, and Angkor Wat, spanning nearly every major ancient civilization.
The Egg-Balancing Myth
A persistent legend claims you can balance a raw egg on its end only during the vernal equinox, supposedly because gravitational forces are uniquely aligned. There is no truth to this. The equinox involves no change in gravitational pull that would make an egg easier to balance. You can stand an egg on its end any day of the year with enough patience. The trick works because tiny bumps on the shell create a small platform, not because of any celestial geometry.