Old Farmer’s Almanac
Welcome, fall. The autumnal equinox — also called the September equinox or the fall equinox — arrives Monday.
Not only do temperatures drop, but plant life slows down, and so do people.
When Is the First Day of Fall 2025?
The fall equinox and the first day of autumn arrive Monday at 1:19 p.m. CDT in the Northern Hemisphere. The equinox occurs at the same moment worldwide.
What Is the Autumnal Equinox?
The autumnal equinox is an astronomical event that marks the start of autumn (or fall). In the Northern Hemisphere, the autumnal equinox occurs in September; in the Southern Hemisphere, it occurs in March.
What Is an Equinox?
During an equinox, the sun crosses what we call the “celestial equator” — an imaginary extension of Earth’s equator line into space. The equinox occurs precisely when the sun’s center passes through this line.
For those in the Northern Hemisphere, when the sun crosses the equator going from north to south, this marks the autumnal equinox; when it crosses from south to north, this marks the vernal equinox. In the Southern Hemisphere, it’s the reverse.
After the autumnal equinox, days become shorter than nights as the sun continues to rise later and nightfall arrives earlier. This ends with the winter solstice, after which days start to grow longer once again.
The word “equinox” comes from the Latin aequus, meaning “equal,” and nox, “night.” On the equinox, day and night are roughly equal in length.
The Harvest Moon and Its Connection to Fall
One of our favorite pieces of trivia surrounding the autumnal equinox involves its relationship with the full moon. Curiously, the full moon that occurs nearest to the autumnal equinox is always called the Harvest Moon. Why is that?
Surprise, surprise: the name has to do with farming. Around the fall equinox, the full moon rises around sunset for several nights in a row, traditionally providing farmers with just enough light to finish their harvests before the killing hard frosts of fall set in.
Typically, the moon rises about an hour later each night, but around the time of the fall equinox, the angle of the moon’s orbit and the tilt of the Earth line up just right and cause the moon to rise only about 20 to 30 minutes later each night for several nights in a row.
An Astronomical Moon Name
The Harvest Moon is one of only two moon names that are astronomical terms and aren’t tied to one specific month. Because the full moon nearest to the equinox is always called the Harvest Moon, either September’s or October’s full moon can take on the name. (The other astronomical moon name is the Hunter’s Moon, which is the full moon that directly follows the Harvest Moon. It can occur in either October or November.)
Fall Foliage
Note that fall foliage isn’t due to current weather conditions. This is a common misconception. Leaves change color because of the amount of daylight and photosynthesis.
Signs of Autumn: Nature, Weather, and Traditions
What are your local signs of fall? In many regions of the Northern Hemisphere, the landscape silently explodes with vibrant colors of red, yellow, and orange.
The leaves begin to drop off the trees, providing endless hours of jumping into leaf piles for kids — and raking up for parents.
Trees snapping and cracking in the autumn indicate dry weather.
Fall also brings some wonderful holidays, including Halloween and Thanksgiving, which carry us through the season until temperatures begin to drop, nights begin to get longer, and all the woodland critters start storing up for the long haul of winter.
And don’t forget about the end of Daylight Saving Time, when we “fall” back, setting our clocks back one hour and regaining an hour of precious sleep.
Plants and trees are slowing down to get ready for the colder season ahead as sunlight decreases. In the garden, asters and chrysanthemums bloom beautifully as orange pumpkins and corn mazes abound.
Football season is warming up, and so is sweater weather.
Also, notice the arc of the sun across the sky each day as it starts shifting south. Birds and butterflies migrate along the path of the sun.
Of course, you can you can easily notice the later dawns and earlier sunsets.
Another definition of fall is: nights of below-freezing temperatures combined with days of temperatures below 70°F (21°C). From here on out, the temperatures begin to drop.
