First day of fall: Why the equinox isn’t as equal as you might think

CNN  — 

Twice a year, everyone on Earth is seemingly on equal footing – at least when it comes to the distribution of daytime and nighttime.

We’ve entered our second and final equinox of 2022. If you reside in the Northern Hemisphere, you know it as the fall equinox (or autumnal equinox). For people south of the equator, this equinox actually signals the coming of spring.

Folks right along the equator have roughly 12-hour days and 12-hour nights all year long, so they won’t really notice a thing on September 22.

But during equinoxes, everyone from pole to pole gets to enjoy a 12-hour split of day and night. Well, there’s just one rub – it isn’t as perfectly “equal” as you may have thought.

There’s a good explanation (SCIENCE!) for why you don’t get precisely 12 hours of daylight on the equinox. More on that farther down.

But first, here are the answers to your other burning equinox questions:

Where does the word ‘equinox’ come from?

From our CNN Fast Facts file: The term equinox comes from the Latin word equinoxium, meaning “equality between day and night.”

Precisely when does the fall equinox happen?

The sun rises behind the Washington Monument in the US capital.

The exact time depends on whom you ask. The equinox will arrive at 1:03 UTC (Coordinated Universal Time) Friday, September 23, according to NASA and However, it will be 1:04 UTC according to the Royal Museums Greenwich and the US National Weather Service.

For people in places such as Toronto and Washington, DC, that’s 9:03 p.m. local time. It comes at 8:03 p.m in Mexico City and Chicago. Out West in San Diego and Vancouver, that means it arrives at 6:03 p.m.

But go in the other direction across the Atlantic Ocean, and the time change puts you into Friday. For residents of Madrid, Berlin and Cairo, it comes at 3:03 a.m. Friday. Going farther east, Dubai marks the exact event at 5:03 a.m.

For residents of Bangkok, it’s 8:03 a.m. while Tokyo clocks in at 10:03 a.m. You can click here to see more cities (rounded down by one minute and adjusted for Daylight Saving Time).

Is the autumn equinox the official first day of fall?

Autumn in northern Germany shows its beautiful side at the Ludwigslust Canal at  Ludwigslust Palace. This photograph was taken on November 2, 2020, which lands within astronomical fall and meteorological fall.

Yes. Fall officially begins on the autumn equinox.

But there are actually two measures of the seasons: “the astronomical seasons” (which follow the arrivals of equinoxes and solstices) and what’s called the “meteorological seasons.”

Allison Chinchar, CNN meteorologist, explains the differences:

“Astronomical fall is essentially the time period from the autumnal equinox up to the winter solstice. Those dates can vary by a day or two each year,” she says.

“Meteorological fall is different … in that the dates never change and are based on climatological seasons rather than Earth’s angle relative to the sun. These are perhaps the seasons that more people are familiar with,” Chinchar says.

Meteorological seasons are defined as the following: March 1 to May 31 is spring; June 1 to August 31 is summer; September 1 to November 30 is autumn; and December 1 to February 28 is winter.

“This makes some dates tricky,” Chinchar says. “For example, December 10, most people would consider winter, but if you are using the astronomical calendar, technically that is still considered autumn because it is before the winter solstice.”

She said that “meteorologists and climatologists prefer to use the ‘meteorological calendar’ because not only do the dates not change – making it easy to remember – but also because it falls in line more with what people think traditional seasons are.”