The autumnal equinox or September equinox falls on September 22. Here’s everything you need to know about the equinox and signs of the equinox in nature.
When is the Autumnal Equinox?
Specifically, the Northern Hemisphere marks the autumnal equinox on Friday, September 22, 2017, at exactly 4:02 P.M. EDT.
|Year||Autumnal Equinox (Northern Hemisphere)|
|2017||Friday, September 22|
|2018||Saturday, September 22|
|2019||Monday, September 23|
What is the Autumnal Equinox?
The Autumnal equinox—also called the September equinox—is the astronomical start of fall in the Northern Hemisphere and spring in the Southern Hemisphere.
The word equinox comes from the Latin aequus (equal) and nox (night).
During the equinox, the Sun crosses what we call the “celestial equator” (just imagine the line that marks the equator on Earth extending up into the sky) from north to south.
Earth’s two hemispheres are receiving the Sun’s rays about equally. The Sun is overhead at noon as seen from the equator. At this point, the amount of nighttime and daytime (sunlight) are roughly equal to each other.
Another definition of fall is nights of below-freezing temperatures combined with days of temperatures below 70 degrees Fahrenheit. From here on out, the temperatures begin to drop and the days start to get shorter than the nights.
It is the summer’s great last heat,
It is the fall’s first chill: They meet.
–Sarah Morgan Bryan Piatt
What’s in store for your winter weather? Order your copy of The Old Farmer’s Almanac!
Why Aren’t Days and Nights Equal?
Nights and days actually aren’t perfectly equal on the equinox, as in 12 hours of daylight and 12 hours of nighttime. The split may be off by a few minutes. Why does this happen?
It depends on where you live. On the autumnal and vernal equinoxes, the very center of the Sun sets just 12 hours after it rises. But the day begins when the upper edge of the Sun reaches the horizon (which happens a bit before the center rises), and it doesn’t end until the entire Sun has set. Not only that, but the Sun is actually visible when it is below the horizon, as Earth’s atmosphere refracts the Sun’s rays and bends them in an arc over the horizon.
According to our former Almanac astronomer, George Greenstein, “If the Sun were to shrink to a star-like point and we lived in a world without air, the spring and fall equinoxes would truly have ‘equal nights.’”
Does the Sun rise due east and set west at the equinox? See more odd equinox facts from astronomer Bob Berman!
What Falling Leaves Indicate
There’s an old weather proverb that states, “If autumn leaves are slow to fall, prepare for a cold winter.” This means that leaves that hang onto the tree indicate a colder winter to come. Or, perhaps you just haven’t had enough windy days! But look on the bright side—you get to look at the beautiful autumn foliage for a little bit longer. Learn why autumn leaves change color.
Signs of Fall
In many regions of North America, 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 them back up for parents!
Plants and trees are slowing down, as sunlight decreases. However, in the garden, asters and chrysanthemums bloom beautifully as orange pumpkins and corn mazes abound. Baseball season hits the homestretch, while football season is just warming up.
Of course, you can you can easily notice the later dawns and earlier sunsets. See our sunrise/set tool for your backyard!
Also, notice the arc of the sun across the sky each day as it starts shifting south. Birds and butterflies migrate along with the path of our Sun!
How do you know that fall is coming? Share your ideas in the comments below!
New England Aster.
Autumn Folklore and Verse
Autumn days come quickly, like the running of a hound on the moor. –Irish proverb
Trees snapping and cracking in the autumn indicate dry weather.
If, in the fall of the leaves in October, many of them wither on the boughs and hang there, it betokens a frosty winter and much snow.
Spring rain damps;
Autumn rain soaks.
Of autumn’s wine, now drink your fill; the frost’s on the pumpkin, and snow’s on the hill.
–The Old Farmer’s Almanac, 1993
Autumn has caught us in our summer wear. –Philip Larkin, British poet (1922–86)
To learn more about the four seasons and see when they begin, see First Day of Seasons.