What Is The Autumn Equinox? Six Key Questions, Answered

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Today, the autumn equinox will occur. Contrary to popular belief, the equinox isn’t a day-long event – it’s one short moment that officially marks the transition between summer and fall. In fact, it already happened earlier today.

What other misconceptions are there about the autumn equinox? What else should you know about the equinox? Learn all about it below.

1. If it’s not a full day, what is the autumn equinox?

The autumn equinox occurs exactly when the sun crosses the celestial equator (which is basically Earth’s equator projected into space). This moment is fleeting, far from an all-day occurrence. At this one short moment in time, the earth’s tilt is at a right angle from the sun, which theoretically results in equal amounts of daytime and nighttime. However, it’s rare that this equality is ever actually achieved.

2. Why is it called the autumn equinox?

The “autumn” part speaks for itself, but the word “equinox” may be unfamiliar. Its roots are in the Latin words “aequus” (“equal”) and “nox” (“night”). Thus, the word “equinox” roughly means “equal night.” This description is fair enough if applied solely to the sun’s crossing of the celestial equator, but since there are roughly eight more minutes of daylight than nighttime on the day of the equinox, it’s imperfect. Learn more about the earth’s relationship with the sun – which dictates the changing of seasons and more – here.

3. At what time does the autumn equinox occur?

The autumn equinox doesn’t occur at any one set time – it varies by year. This year’s autumn equinox happened earlier today, at 3:50 am EDT. 

4. When doesn’t the autumn equinox occur?

The autumn equinox tends to occur on September 22nd or, as with today, September 23rd. It’s extremely rare, but not impossible, that the autumn equinox can occur on September 21st or September 24th. However, a September 21st autumn equinox hasn’t happened in literally thousands of years, and it won’t again until 2092. A September 24th autumn equinox occurred a bit more recently, in 1931, but it won’t happen again until 2303.

5. Is the autumn equinox related to Daylight Saving Time?

Since the onset of fall eventually leads to the arrival of Daylight Saving Time, some people ask whether the autumn equinox relates to Daylight Saving Time. The two events are unrelated, as the equinox is a natural occurrence and Daylight Saving Time is a manmade system. This year, Daylight Saving Time ends on Sunday, November 3rd, when everybody’s clocks will fall back one hour and days will feel shorter.

6. What else does the autumn equinox bring?

According to NASA, after the autumn equinox, the chances of seeing an aurora borealis (northern lights) will increase. The climate and astronomical conditions that follow the autumn equinox increase the likelihood of the geomagnetic activity that causes aurora borealis, overall doubling the chances of northern lights. It’s still not like northern lights will be possible to see from most urban areas, though – try traveling much farther north for that. 

What are you doing to celebrate the arrival of fall? Sound off in the comments!