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Thursday (March 20) marks the start of the spring season for the Northern Hemisphere and fall in the Southern Hemisphere, with the arrival of the vernal equinox.
On this day, the sun appears directly above the Equator at noon.
Equinoxes occur twice a year, in March and in September, and are the only times when both poles are sunlit at the same time.
In the Northern Hemisphere, the vernal or spring equinox, typically occurs between March 19 and 21, while the autumnal or fall equinox occurs between September 21 and 24. The names are switched for the Southern Hemisphere, so March 20, 2025, marks the autumnal equinox there.
The term is derived from the Latin words “aequus” meaning “equal”, and “nox” (meaning “night”).
Equinoxes reflect the time of the year when the day and night are of equal length.
On all other days, the Earth’s axis is tilted either towards or away from the sun. This impacts how the light and the warmth of the sun are distributed across the hemispheres.
During the equinox, the Earth’s axis and orbit align just so that both hemispheres obtain an equal amount of sunlight.
Solstices mark the days when the Earth is extremely tilted toward or away from the sun. On these days, each hemisphere gets significantly different amounts of light and warmth from the sun, with the days and nights being just as lopsided.
The summer solstice in the Northern Hemisphere, between June 20 and 22, creates the longest day and shortest night of the year, as the upper half of the earth is tilted towards the sun.
Conversely, the winter solstice in the Northern Hemisphere, between December 20 and 23, creates the shortest day and longest night of the year, with the upper half of the earth is tilted towards the sun.
The ancient Babylonian calendar began the first full moon following the March equinox, in a tradition that has been carried forward by many cultures celebrating new year in the spring.
The Persian new year, Nowruz, coincides with the vernal equinox in the northern hemisphere. The festival has been observed for over 3,000 years by followers of Zoroastrianism globally, including the Parsi community in India. Nowruz begins on the first day of the Farvardin, the first month of the Iranian solar calendar at the spring equinox, and continues for 12 days.
The Vernal Equinox Day is a national holiday in Japan, while Easter, one of the most important days in the Christian calendar, is determined according to the vernal equinox. In the Jewish calendar, Passover, the Jewish festival begins on the first full moon following a vernal equinox.
The autumnal equinox on the other hand sees the observance of autumnal harvest festivals, such as Chuseok, celebrated over three days in both Koreas. The Rosh Hashanah and Yom Kippur, two of the holiest days of the Jewish calendar, fall in this period. Rosh Hashanah, the Jewish new year, is calculated as 163 days after the first day of Passover, while Yom Kippur, the “Day of Atonement” is usually observed ten days later.
