Fall is here
The first day of Fall was, Monday, September 23. On this day, fall begins in the Northern Hemisphere and spring begins in the Southern Hemisphere. Wondering why it’s called an equinox? Here’s all you need to know.
What is the Autumnal Equinox?
Autumn days come quickly, like the running of a hound on the moor.
The autumnal equinox—also called the September or fall equinox—is the astronomical start of the fall season in the Northern Hemisphere and the spring season in the Southern Hemisphere.
What is an Equinox?
The word “equinox” comes from Latin aequus, meaning “equal,” and nox, “night.” On the equinox, day and night are roughly equal in terms of length. (See more about this below.)
During the equinox, the Suncrosses what we call the “celestial equator”—an imaginary extension into space of Earth’s equator line. The equinox occurs precisely when the Sun’s center passes through this line. When the Sun crosses the equator from north to south, this marks the autumnal equinox; when it crosses from south to north, this marks the vernal equinox.
Fall Equinox FAQs
Q: Are Day and Night Perfectly Equal on the Equinox?
A: As say that during an equinox, day and night is equal. Well, not exactly. It depends where you live.
On the equinox, the center of the Sun is indeed above the horizon for 12 hours. However, “sunrise” is said to begin when the upper edge of the Sun’s disk becomes visible above the horizon (which happens a bit before the center rises) and ends when the entire Sun has set. In this case, daylight is still a bit longer than nighttime.
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. Yes, you can see the Sun before the edge actually reaches the horizon! This causes daylight to be longer than 12 hours as well.
However, they are very close to equal (the lengths may be off by only a few minutes).
Did you know our rise/set tool now provides day length? In Dublin, New Hampshire—home of The Old Farmer’s Almanac—our day length on the equinox is 12:08 hours.
See our Sunrise/set calculator for day length in YOUR area.
Q: Is the Autumnal Equinox Really the First Day of Fall?
A: Based on the astronomical definition of seasons, yes, the autumnal equinox does mark the first day of fall (in the Northern Hemisphere). However, according to the meteorological definition of seasons, which is based on temperature cycles and the Gregorian calendar, the first day of fall is September 1.