The vernal equinox will take place on Thursday, 20 March 2025, marking the official start of spring in the Northern Hemisphere. This astronomical event signifies equal daylight and night-time hours due to the Earth’s position in its orbit around the Sun.
Equinox: A Balance of Light and Darkness
The word equinox originates from Latin, meaning “equal night”. During this phenomenon, the Sun is directly overhead at the Earth’s equator at noon, causing almost equal distribution of sunlight worldwide. Both hemispheres experience similar daylight hours as the Earth’s axis aligns perpendicularly to the Sun’s rays.
Equinoxes occur twice a year—in March and September—dividing the astronomical seasons into spring and autumn.
Figure 1: The Equinox
How the Equinox Affects Global Seasons
For the Northern Hemisphere, the vernal equinox signals the transition from winter to spring. Meanwhile, in the Southern Hemisphere, it marks the beginning of autumn. The next autumnal equinox will occur between 21 and 24 September 2025.
During this period, daylight gradually increases in the Northern Hemisphere and decreases in the Southern Hemisphere, leading to seasonal weather changes.
Equinox and Its Role in Cultural Traditions
Throughout history, civilisations have observed the equinox as a significant seasonal milestone. In Iran, the equinox marks Nowruz, the Persian New Year, a tradition that has been celebrated for over 3,000 years.
At Chichen Itza, Mexico, visitors gather to witness a unique shadow illusion on El Castillo, a Mayan pyramid. The play of sunlight creates the appearance of a serpent slithering down the steps, symbolising the deity Kukulkan.
Equinox Compared to the Solstice
Equinoxes occur when the Earth’s axis is neither tilted toward nor away from the Sun. In contrast, solstices represent the Sun’s most extreme positions relative to the Earth.
- Summer Solstice (June 20-22, 2025): The longest day of the year in the Northern Hemisphere when the Sun is at its highest point.
- Winter Solstice (December 20-23, 2025): The shortest day of the year when the Sun is at its lowest point in the sky.
Figure 2: Equinox compared to the Solstice
Astronomical vs Meteorological Seasons
Astronomical seasons follow Earth’s position relative to the Sun, while meteorological seasons align with temperature patterns.
- Meteorological Spring: Begins 1 March and ends 31 May.
- Astronomical Spring: Begins with the equinox on 20 March and lasts until the summer solstice in June.
The National Oceanic and Atmospheric Administration (NOAA) states that astronomical seasons rely on Earth’s orbit, whereas meteorological seasons use climate-based cycles.
Figure 3: Brief differentiation between Astronomical and Meteorological Seasons
Why the Equinox Date Changes
The vernal equinox does not always fall on 21 March. Depending on Earth’s orbit and leap years, it occurs between 19 and 21 March.
The Old Farmer’s Almanac notes that the United States has not had a 21 March equinox in the 21st century. The next one will occur in 2101.
Scientific Explanation of the Equinox
The scientific community explains that the equinox occurs due to Earth’s axial tilt of 23.5 degrees. When Earth reaches a specific orbital position, sunlight distributes evenly between the hemispheres.
The National Weather Service (NWS) states:
“Equinoxes are the only two times of the year when the Earth’s axis isn’t tilted toward or away from the sun.”
Impact of the Equinox on Weather
Weather patterns shift following the equinox due to changing solar exposure. The El Niño-Southern Oscillation (ENSO) phenomenon affects spring weather conditions.
The National Oceanic and Atmospheric Administration (NOAA) predicts:
- A 34% chance that La Niña will extend into spring 2025.
- If La Niña continues, the U.S. may experience increased tornado activity and large hail events from March to May.
The Farmers’ Almanac forecasts:
- A “Thunder and Zing Spring” across most of the United States.
- Texas, Oklahoma, and the Great Plains will experience warm and dry conditions.
- Texas will start spring with cooler-than-normal temperatures before shifting to above-average warmth in May.
Figure 4: The Farmer’s Almanac Forecast
How the Equinox Affects Daylight Hours
During the equinox, the Sun rises exactly in the east and sets exactly in the west.
However, day and night are not perfectly equal due to:
- Atmospheric Refraction: The Sun’s rays bend, making the Sun visible even when it is slightly below the horizon.
- Sun’s Angular Size: The Sun appears as a disk rather than a point, causing the upper part of the Sun to rise before the lower part has set.
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Future Equinox Dates
The next spring equinox will occur on 20 March 2026, continuing the annual shift within the March 19-21 range.
The next autumnal equinox will take place on 23 September 2025, marking the transition from summer to autumn in the Northern Hemisphere.
Significance of the Spring Equinox
The spring equinox symbolises renewal and transformation in many cultures. Some people participate in spiritual rituals, including:
- Balance and harmony practices inspired by the equal length of day and night.
- Cleansing ceremonies aimed at purifying the body and mind.
- Seasonal festivals celebrating new growth and warmer days ahead.
Conclusion
The spring equinox of 2025 officially begins a new astronomical season. This event highlights the Earth’s movement, cultural traditions, and seasonal changes. With warmer days ahead, the equinox continues to mark a significant shift in daylight, weather, and human activity worldwide.
