How Many Days Until the Autumn Equinox?
The Autumn Equinox 2025 occurs around Monday, September 22, 2025.
About the Autumn Equinox
The Autumn Equinox, also known as the Fall Equinox or September Equinox, is an astronomical event that marks the beginning of autumn (fall) in the Northern Hemisphere and spring in the Southern Hemisphere. It occurs when the Sun shines directly on the Earth's equator, resulting in nearly equal lengths of day and night across the globe. This typically happens around September 22nd or 23rd each year.
The Science of the Equinox
The equinox is defined by the Earth's tilt and its orbit around the Sun.
Earth's Tilt
Earth orbits the Sun on an axis tilted about 23.5 degrees. This tilt causes the seasons. During the equinoxes, the tilt is neither toward nor away from the Sun relative to the equator.
Sun Over the Equator
At the moment of the equinox, the Sun's center passes directly over the Earth's equator. This point is called the subsolar point.
Equal Day and Night? Almost!
"Equinox" means "equal night." While day and night are very close to 12 hours each, atmospheric refraction bends sunlight, making the day slightly longer than the night exactly on the equinox.
Date Variation
The date varies slightly (Sept 21-24) due to the Gregorian calendar's leap year system and the Earth's elliptical orbit.
Cultural Significance and Celebrations
Throughout history, the Autumn Equinox has been a significant time for many cultures:
- Harvest Festivals: Many cultures traditionally celebrated the main harvest around this time, giving thanks for the bounty before winter (e.g., Mabon in Neopaganism, Mid-Autumn Festival in East Asia, Harvest Home in Britain).
- Balance and Transition: The equal day and night symbolize balance. It's seen as a threshold time, transitioning from the outward energy of summer to the inward focus of winter.
- Ancient Monuments: Some ancient structures, like Chichen Itza in Mexico, align with the Sun during the equinoxes, suggesting astronomical and ceremonial importance.
- Michaelmas (Christian): The Feast of St. Michael (September 29th) falls near the equinox and historically marked the end of the harvest season and the beginning of a new business year.
- Higan (Japanese Buddhism): A period surrounding both equinoxes dedicated to remembering ancestors and visiting graves.
The Shift to Autumn
The Autumn Equinox signals noticeable changes in the natural world in the Northern Hemisphere:
Decreasing Daylight
After the equinox, the days become progressively shorter than the nights as the Sun's path moves lower in the sky.
Cooling Temperatures
Average temperatures begin to drop more noticeably, bringing crisp air and the possibility of frost in some regions.
Changing Leaf Colors
Deciduous trees respond to decreasing daylight and cooler temperatures by stopping chlorophyll production, revealing vibrant yellow, orange, and red pigments.
Animal Migration & Preparation
Many bird species begin migrating south. Other animals focus on storing food or preparing dens for winter.