First Day of Autumn

Welcome to the First Day of Autumn Calculator, your comprehensive guide to finding the exact date and time of the autumn equinox for any year from 2000 to 2040. Whether you are planning seasonal activities, studying astronomy, or simply curious about when fall begins, this tool provides accurate equinox data for both the Northern and Southern Hemispheres.

What is the First Day of Autumn?

The first day of autumn, also known as the autumn equinox or fall equinox, marks the astronomical beginning of the autumn season. On this day, the Sun crosses the celestial equator, resulting in approximately equal hours of daylight and darkness worldwide. This event occurs twice a year: in September for the Northern Hemisphere and in March for the Southern Hemisphere.

Astronomical vs Meteorological Autumn

The Four Seasons Cycle

Earth's axial tilt of approximately 23.5 degrees creates the four seasons as our planet orbits the Sun:

Note: The months shown above are for the Northern Hemisphere. In the Southern Hemisphere, seasons are reversed.

Why Does the Autumn Equinox Date Change?

The autumn equinox does not fall on the exact same date every year due to several factors:

• Orbital period: Earth takes approximately 365.25 days to orbit the Sun, not exactly 365 days
• Leap years: The extra day in leap years helps correct the drift but causes date variations
• Precession: Earth's wobble on its axis causes gradual shifts over thousands of years
• Orbital eccentricity: Earth's slightly elliptical orbit affects timing

Autumn Equinox Traditions and Celebrations

Many cultures around the world celebrate the autumn equinox with festivals and traditions:

• Mabon: A modern pagan celebration of the second harvest
• Mid-Autumn Festival: Chinese celebration with mooncakes and lanterns
• Chuseok: Korean harvest festival honoring ancestors
• Thanksgiving (harvest festivals): Celebrations of the harvest season in many countries
• Higan: Japanese Buddhist holiday for honoring ancestors

Frequently Asked Questions

When is the first day of autumn 2025?

The first day of autumn 2025 in the Northern Hemisphere falls on Monday, September 22, 2025, at 18:19 UTC. This is the autumn equinox, when day and night are approximately equal in length. In the Southern Hemisphere, autumn 2025 begins on March 20, 2025.

What is the difference between the autumn equinox and meteorological autumn?

The astronomical autumn begins at the autumn equinox (around September 22-23 in the Northern Hemisphere), determined by Earth's position relative to the Sun. Meteorological autumn, used by weather services, always begins on September 1 and ends on November 30 in the Northern Hemisphere, based on temperature cycles and calendar months.

Why does the first day of autumn change each year?

The autumn equinox date varies slightly each year because Earth's orbit around the Sun takes approximately 365.25 days, not exactly 365 days. This fractional day causes the equinox to occur at different times, and leap years help correct this drift. The equinox can fall on September 21, 22, 23, or rarely 24.

Is autumn the same as fall?

Yes, autumn and fall refer to the same season. "Fall" is primarily used in American English, derived from "fall of the leaf." "Autumn" is more common in British English and comes from the Latin "autumnus." Both terms describe the season between summer and winter when leaves change color and temperatures cool.

When is autumn in the Southern Hemisphere?

In the Southern Hemisphere, autumn begins around March 20-21 (the March equinox) and lasts until the June solstice (around June 20-21). Countries like Australia, New Zealand, Argentina, and South Africa experience autumn during these months, which is spring in the Northern Hemisphere.

Additional Resources

• Equinox - Wikipedia
• Autumn - Wikipedia