Spring Equinox Marks Global Celebration of Equal Day and Night

TEHRAN, Iran — The vernal equinox arrived on March 19, 2025, officially ushering in spring for the Northern Hemisphere while marking the start of fall in the Southern Hemisphere. On this day, the sun is directly overhead at noon along the equator, and both poles are illuminated by sunlight simultaneously.

This astronomical event has been celebrated for centuries across various cultures. In Iranian tradition, the spring equinox is the foundation of Nowruz, the Persian New Year, which heralds the arrival of spring. Celebrations include the ancient Festival of Fire, Chaharshanbe Souri, where Iranians jump over flames to symbolize purification and the shedding of the old year.

Meanwhile, at the Mayan site of Chichen Itza in Mexico, locals gather during the equinox to witness the sun cast serpent-like shadows down the steps of the pyramid, known as El Castillo. This phenomenon has drawn thousands of visitors eager to witness this display that celebrates the cycle of the seasons and the connection to nature.

The word ‘equinox’ derives from the Latin terms for ‘equal’ and ‘night,’ denoting the balance of day and night at this time of year. The Northern Hemisphere experiences its spring or vernal equinox between March 19 and 21, while the autumnal equinox falls between September 21 and 24.

As Earth orbits the sun at an angle, its axis wobbles, resulting in unequal sunlight distribution across the planet throughout the year. During the equinox, however, Earth’s tilt aligns in such a way that it receives equal sunlight in both hemispheres. Professor Karen McCormick of the National Space Science Center explained, ‘The equinox is a significant reminder of how interconnected our seasonal changes are to the motion of Earth.’

The summer solstice, which occurs between June 20 and 22, represents the longest day and shortest night in the Northern Hemisphere when the tilt leans toward the sun. Conversely, the winter solstice between December 20 and 23 signifies the shortest day and longest night when the axis tilts away from the sun.

These seasonal markers are critical not only for cultural traditions but also for agricultural practices worldwide. While astronomical seasons are based on Earth’s orbit, meteorological seasons are defined by temperature patterns, with spring commencing on March 1, summer on June 1, fall on September 1, and winter on December 1.

The Associated Press Health and Science Department acknowledges support from the Howard Hughes Medical Institute’s Science Education Media Group for this reporting.