(CNN) – Twice a year, everyone on Earth seems to be on an equal footing – at least when it comes to day and night distribution.
On Saturday we will enter our second 2018 equinox. If you reside in the northern hemisphere, you know it as the autumn equinox (or 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 a night all year, so they will not see much on September 22nd.
People close to the poles, in destinations such as Alaska, suffer every year from strong fluctuations in the day / night ratio. They have long winters and dark summers where the night hardly infiltrates.
But during the equinox, everyone, from pole to pole, enjoys a distribution of day and night of 12h. Well, there is just one rub – it's not as perfectly "equal" as you may have thought.
There is a good explanation (SCIENCE!) For which you do not get precisely 12 hours of day on the equinox. More on that further down in the article.
Here are the answers to some of your autumn equinox questions:
Where does the word "equinox" come from?
From our CNN Fast Facts file: The term equinox comes from the Latin word equinoxium, which means "equality between day and night".
When is it?
In 2018, he falls on Saturday, September 22nd. It is actually a precise time: 1h54 UTC. (UTC stands for Coordinated Universal Time.)
That time is converted to 21:54 ET in the United States. Here is a handy online tool for converting UTC to local time.
Why does the autumnal equinox occur?
The Earth turns on an imaginary line that goes from the North Pole to the South Pole. This is called the axis, and this rotation is what gives us the day and the night.
However, the axis switches to 23.5 degrees, as NASA indicates. This positions one hemisphere of the planet to get more light than the other during half of the year orbit around the sun. This shift in the sunlight is what sets off the seasons.
The effect is at its maximum end of June and end of December. These are the solstices, and they have the most extreme differences between day and night, especially near the poles. (That's why it stays so light every day during the summer in countries like Scandinavia.)
Since the summer solstice in June, days have become shorter and shorter in the northern hemisphere and longer nights in the last three months. Welcome to the autumn equinox!
What did our ancestors know?
A "superhenge" discovered near Stonehenge in England is believed to have been built 4,500 years ago. CNN reports Erin McLaughlin.
Well before the age of clocks, satellites and modern technology, our ancient ancestors knew a lot about the movement of the sun across the sky – enough to build gigantic monuments and temples that served as giant calendars to mark seasons. .
You can travel to these sites today. Here are a few:
– The megalithic temples of Malta: these seven temples on the Mediterranean island are among the oldest stone buildings in the world, 5,000 to 6,000 years ago. In the Hagar Qim and Mnajdra temples, the semicircular chambers are aligned so that the rising sun on the equinox is framed between the stones.
– Jantar Mantar (New Delhi, India): Much more recent (1724 and 1730), these buildings dating from the end of the Mughal period are astronomical observatories. The crowds will gather here each equinox (though they make a fascinating tour anytime).
What are some festivals, myths and rituals still with us?
Around the world, the autumn equinox is imposed in our cultures and celebrations.
In Greek mythology, the autumnal equinox marks the return of the goddess Persephone to hell for three months, where she finds her husband, Hades.
The Chinese and Vietnamese continue to celebrate the Harvest Moon (also known as the Mid-Autumn Festival). Lanterns line the streets as people thank, look at the moon and eat. Round pastries called mooncakes are a favorite of the Mid-Autumn festival. It takes place on the 15th day of the eighth lunar month of the Chinese calendar. It's Monday, September 24, 2018.
Harvest festivals in Britain have their roots in the autumnal equinox since the pagan era. Some of the many offers:
– Harvest Festival at Bowhill House (September 30, 2018): In Scotland, this festival showcases some aspects of forestry (woodturning, horse-cutting). (Bowhill House, Bowhill, Selkirk, Scottish Borders, TD7 5ET: +44 1750 22204)
– RHS Harvest Festival Show (2-3 October 2018): See giant pumpkin and heavier apple competitions. Enjoy tastings and learn how to grow autumn vegetables. (Lindley Hall, Elverton Street, London SW1P 2PB, United Kingdom, +44 20 7821 3650)
Are aurora borealis really more active at equinoxes?
In a word, yes.
It turns out that the autumn equinox and the spring (or spring equinox) usually coincide with maximum activity with the northern lights.
So why is the equinox not exactly equal?
It turns out that the equinox is slightly sunnier than dark, depending on where you are on the planet. How's it going?
As the US National Weather Service explains, the "almost" equal hours of day and night are due to the complex way of measuring sunrise and the refraction of sunlight in our atmosphere.
This bending "causes the sun to appear over the horizon when the actual position of the sun is below the horizon." The day is a little longer at higher latitudes than at the equator because it takes longer for the sun to rise and get closer to the poles. So, at the autumnal equinox, the length of day will vary slightly depending on where you are:
– At the equator: about 12 hours and 6 and a half minutes (Quito, Ecuador or Kampala, Uganda)
– At 30 degrees latitude: about 12 hours and 8 minutes (Austin, Texas or Cairo, Egypt)
– At 60 degrees of latitude: approximately 12 hours and 16 minutes (Helsinki, Finland)
