(CNN) – Twice a year, everyone on Earth seems to be on an equal footing, at least when it comes to the distribution of light and dark.
On Tuesday we enter our second and final equinox of 2020. If you reside in the northern hemisphere, you know it as the autumnal equinox. For people south of the equator, this equinox actually signals the arrival of spring.
People along the equator have about 12 hours a day and 12 hours at night throughout the year, so they don’t really notice anything. But people near the poles, in places like northern Canada, Norway and Russia, experience sudden changes in the day / night ratio every year. They have dark winters and long summers where the night barely peeks out.
But during the equinoxes, everyone, from one pole to another, can enjoy a 12/12 split day and night. Well, there’s only one thing: it’s not as perfectly “the same” as you might have thought.
There is a good explanation (SCIENCE!) Why you don’t get exactly 12 hours of light at the equinox.
Here are the answers to your questions about the autumnal equinox:
Where does the word ‘equinox’ come from?
From our CNN Fast Facts archive: The term equinox comes from the Latin word equinoxium, which means “equality between day and night.”
Exactly when does the autumnal equinox occur?
The equinox will arrive at 13:31 UTC (coordinated universal time) on September 22. For people in places like Toronto and Miami, it’s 9:31 a.m. local time. In Los Angeles and Vancouver, that means it arrives at 6:31 a.m.
Now, for the people of Madrid, Berlin, and Cairo, it arrives at precisely 3:31 p.m. Going further east, Dubai marks the exact event at 5:31 p.m. For Bangkok residents, it’s 8:31 p.m. while Singapore and Hong Kong register at 9:31 pm. You can click here to see more cities (rounded down in a minute).
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Why does the autumnal equinox occur?
The Earth rotates along an imaginary line that goes from the North Pole to the South Pole. It is called the axis, and this rotation is what gives us day and night.
However, the axis is tilted at 23.5 degrees, as NASA explains. That positions one hemisphere of the planet to get more sunlight than the other for half the orbit of the year around the Sun. This discrepancy in sunlight is what triggers the seasons.
The effect reaches its maximum in late June and late December. Those are the solstices and they have the most extreme differences between day and night, especially near the poles. (This is why they stay lit for so long every day during the summer in places like Scandinavia and Alaska.)
But since the summer solstice three months ago in June, you’ve noticed that our days have progressively shortened in the Northern Hemisphere and the nights are longer. And here we are at the autumnal equinox!
What did our ancestors know about all this?
Long before the age of clocks, satellites, and modern technology, our ancestors knew a great deal about the movement of the Sun across the sky. Enough to build massive monuments and temples that, among other purposes, served as giant calendars to mark the seasons.
Normally, you could organize trips to these places. This year, you should consider the covid-19 pandemic as you would any other trip.
These are just a few of the sites associated with the equinox:
– Stonehenge (UK): Many mysteries remain about these giant slabs, but we know they are lined up to mark the annual passage of the Sun. Due to the pandemic, there will be no in-person meeting at Stonehenge this fall, according to the BBC.
– Megalithic temples of Malta: These seven temples on the Mediterranean island are some of the world’s first freestanding stone buildings, dating back 5,000 to 6,000 years ago. In the temples of Hagar Qim and Mnajdra, the semicircular chambers are aligned so that the Sun rising on an equinox is framed between the stones.
– Jantar Mantar (New Delhi, India): Of much more recent origin (1724 and 1730), these buildings from the end of the Mughal period are astronomical observatories.
READ: They discovered a huge new prehistoric circle near Stonehenge
What are some festivals, myths and rituals that still accompany us?
Around the world, the autumnal equinox has made its way into our cultures and traditions.
In Greek mythology, the autumnal equinox marks the return of the goddess Persephone to the underworld for three months, where she is reunited with her husband, Hades.
The Chinese and Vietnamese still celebrate the Harvest Moon (also known as the Mid-Autumn Festival). Lanterns line the streets as people give thanks, look at the moon, and eat. Round cakes called mooncakes are a Mid-Autumn Festival favorite. It takes place on the 15th day of the eighth lunar month in the Chinese calendar. It will be on Thursday, October 1 of this year.
Britain’s beloved harvest festivals have their roots in the autumnal equinox since pagan times.
In Japan, the Autumn Equinox Day is a national holiday. In Japanese, it is known as Shubun no Hi (秋分 の 日), according to the Coto Japanese Academy. The roots of the celebration are believed to go back to Shintoism and Buddhism.
Are the Northern Lights really more active on the equinoxes?
Yes, they often put on more show at this time of year.
It turns out that the autumnal equinox and spring (or vernal equinox) generally coincide with the peak activity of the northern lights.
These beautiful and fascinating geomagnetic storms tend to be most active in March and April and then again in September and October, according to 75 years of historical records analyzed by solar physicist David Hathaway of the Marshall Space Flight Center in Huntsville, Alabama.
So why isn’t the equinox exactly the same?
Turns out, you actually get a little more daylight than darkness at the equinox, depending on where you are on the planet. How does that happen? The answer is a bit complicated but fascinating.
As the US National Weather Service explains, the “almost” equal hours of day and night are due to the complex way in which sunrise and the refraction of sunlight in our atmosphere are measured.
This curvature of the light rays “causes the Sun to appear above the horizon when the actual position of the Sun is below the horizon.” The day is slightly longer at higher latitudes than at the equator because the Sun takes longer to rise and set the closer you get to the poles.
So on the autumnal equinox, the length of the day will vary a bit depending on where you are. Here are some breakdowns to give you an idea:
– At the equator: Approximately 12 hours and 6 and a half minutes (Quito, Ecuador; Nairobi, Kenya; and Singapore are all close to the equator)
– At 30 degrees latitude: Approximately 12 hours and 8 minutes (Houston, Texas; Cairo, Egypt; and Shanghai, China)
– At 60 degrees latitude: Approximately 12 hours and 16 minutes (Helsinki, Finland; and Anchorage, Alaska)
For an equal day / night split, you must wait one day after the official equinox. That day is called equilux, and it is Wednesday, September 23 of this year.