Autumn Equinox: The Science Behind the First Day of Fall

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iStock

On September 22, the Sun will shine directly over the equator—the midpoint of the Earth. (For 2018, this moment will happen at 9:54 p.m. ET.) The whole world will thus experience a day and night of equal length. In the Northern Hemisphere, we call this the autumn equinox. It marks the first day of fall. Around the world, people are marking the day with ceremonies, some of them ancient (and some less so).

You might be wondering two things: 1. Why on almost every other day of the year (the vernal equinox being the other exception) do different parts of the world have days and nights of differing length? 2. What do they call the day in the Southern Hemisphere?

A DAY AT THE BEACH

The answer to each of these questions resides in the Earth's axial tilt. The easiest way to imagine that tilt is to think about tanning on the beach. (Stay with me here.) If you lay on your stomach, your back gets blasted by the Sun. You don't wait 30 minutes then flop over and call it a day. Rather, as you tan, every once in a while, you shift positions a little. Maybe you lay a bit more on one side. Maybe you lift a shoulder, move a leg a little. Why? Because you want the Sun to shine directly on a different part of you. You want an even tan.

It might seem a little silly when you think about it. The Sun is a giant fusion reactor 93 million miles away. Solar radiation is hitting your entire back and arms and legs and so on whether or not you adjust your shoulder just so. But you adjust, and it really does improve your tan, and you know this instinctively.

People light candles during the autumn equinox celebration at Neris River waterfront in Vilnius, Lithuania after sunset on September 21, 2013.
People light candles during the autumn equinox celebration at Neris River waterfront in Vilnius, Lithuania after sunset on September 21, 2013.
PETRAS MALUKAS, AFP/Getty Images

The Earth works a lot like that, except it's operating by physics, not instinct. If there were no tilt, only one line of latitude would ever receive the most direct blast of sunlight: the equator. As the Earth revolved around the Sun, the planet would be bathed in sunlight, but it would only be the equator that would always get the most direct hit (and the darkest tan). But the Earth does have a tilt. Shove a pole through the planet with one end sticking out the North Pole and one end sticking out the South, and angle the whole thing by 23.5 degrees. That's the grade of Earth's tilt.

Now spin our little skewered Earth and place it in orbit around the Sun. At various points in the orbit, the Sun will shine directly on different latitudes. It will shine directly on the equator twice in a complete orbit—the fall and spring equinoxes—and at various points in the year, the most direct blast of sunlight will slide up or down. The highest latitude receiving direct sunlight is called the Tropic of Cancer. The lowest point is the Tropic of Capricorn. The poles, you will note, are snow white. They have, if you will, a terrible tan—and that's because they never receive solar radiation from a directly overhead Sun (even during the long polar summer, when the Sun never sinks below the horizon).

WHEN DO THE SEASONS CHANGE?

A Maya priestess conducts an autumn equinox ceremony at El Salvador's Cihuatan Archeological Park.
A Maya priestess conducts an autumn equinox ceremony at El Salvador's Cihuatan Archeological Park.
Jose CABEZAS, AFP/Getty Images

The seasons have nothing to do with the Earth's distance from the Sun. Axial tilt is the reason for the seasons. The Sun is directly over the Tropic of Cancer (66.5 degrees latitude in the Northern Hemisphere) on June 21 or 22. When that occurs, the Northern Hemisphere is in the summer solstice. The days grow long and hot. As the year elapses, the days slowly get shorter and cooler as summer gives way to autumn. On September 21 or 22, the Sun's direct light has reached the equator. Days and night reach parity, and because the Sun is hitting the whole world head-on, every latitude experiences this simultaneously.

On December 21 or 22, the Sun is directly over the Tropic of Capricorn in the Southern Hemisphere, meaning the Northern Hemisphere is receiving the least sunlight it will get all year. The Northern Hemisphere is therefore in winter solstice. Our days are short and nights are long. Parity will again be reached on March 21 or 22, the vernal equinox for the Northern Hemisphere, and the whole process will repeat itself.

Members of The Druid Order of London conduct a ceremony on Primrose Hill to celebrate the Autumn Equinox on September 22, 2008 in London, England.
Members of The Druid Order of London conduct a ceremony on Primrose Hill to celebrate the Autumn Equinox on September 22, 2008 in London, England. The Druid Order of London, which was founded in Oxford in 1245, has been conducting the Autumn Equinox ceremony on Primrose Hill since 1717.
Matt Cardy, Getty Images

Now reverse all of this for the Southern Hemisphere. When we're at autumnal equinox, they're at vernal equinox. Happy first day of spring, Southern Hemisphere!

And welcome to fall, Northern Hemisphere! Enjoy this long day of sunlight, because dark days are ahead. You'll get less and less light until the winter solstice, and the days will grow colder. Take solace, though, in knowing that the whole world is experiencing the very same thing. Now it's the Southern Hemisphere's turn to get ready to spend some time at the beach.

This story first ran in 2016.

10 Saccharine Facts About Sweetest Day

Peter Purdy, BIPs/Getty Images
Peter Purdy, BIPs/Getty Images

Unless you live in certain parts of the United States, there's a good chance you've never heard of Sweetest Day. For others, however, it's a century-old celebration. Here's what you need to know about the semi-obscure holiday.

1. THERE'S A REASON IT'S THE THIRD SATURDAY IN OCTOBER.

This image of newsboy Emil Frick was first published in The Cleveland Press on October 8, 1921.
This image of newsboy Emil Frick was first published in The Cleveland Press on October 8, 1921.
Digital scan courtesy of The Cleveland Public Library Microform Center, Wikimedia Commons // Public Domain

When the holiday was founded in 1916, trick-or-treating hadn't become popular yet, so though Halloween existed, there was no autumn boost to the candy industry like there is now. That's why the National Confectioners Association invented a mid-season marketing gimmick to help increase sales before Christmas. Naturally, they tried to spin it otherwise, writing that the spirit of the day should be "interpreted as a spirit of good will, appreciation, and good fellowship."

2. IT WAS ORIGINALLY KNOWN AS "CANDY DAY."

A Sweetest Day advertisement first published in The Cleveland Press on October 6, 1921.
A Sweetest Day advertisement first published in The Cleveland Press on October 6, 1921.
Digital scan courtesy of The Cleveland Public Library Microform Center, Wikimedia Commons // Public Domain

Though the National Confectioners Association wanted the celebration to appear as if it was about more than just candy sales, the name they gave the holiday belied their efforts. It didn't become the slightly more subtle "Sweetest Day" until the 1920s.

3. HERBERT HOOVER WAS NOT PLEASED ABOUT IT.

In 1918, Herbert Hoover was the director of the United States Food Administration, and was closely associated with relief efforts Europe. Here, he is standing with his wife and daughter by a poster giving thanks to America for its help in providing food.
In 1918, Herbert Hoover was the director of the United States Food Administration, and was closely associated with relief efforts Europe. Here, he is standing with his wife and daughter by a poster giving thanks to America for its help in providing food.
A. R. Coster, Topical Press Agency/Getty Images

Of course the year the holiday was founded, 1916, was smack in the middle of World War I. By the time the second annual day rolled around, Herbert Hoover, who was then the director of the U.S. Food Administration, reminded the National Confectioners Association that their consumerism creation wasn't exactly in the best interests of America's wartime efforts to conserve sugar.

In 1917, an industry bulletin called The International Confectioner noted, "As Mr. Hoover had requested everyone, everywhere, to cut down as much as possible on their usings of sugar, he considered that Candy Day was an effort on the part of our industry in the very opposite direction."

4. CELEBRITIES AND CAUSE MARKETING FINALLY DID THE TRICK.

Actress Theda Bara giving candy to orphans in 1921.
Actress Theda Bara giving candy to orphans in 1921.
Digital scan courtesy of The Cleveland Public Library Microform Center, Wikimedia Commons // Public Domain

Once it was safe to increase sugar production again, marketing efforts kicked back into high gear. In 1921, Cleveland Candy Day organizers got the bright idea to tie the promotion into charity, giving sweets to orphanages and the elderly. Actresses Theda Bara and Ann Pennington went to Cleveland to help distribute thousands of boxes of candy, which helped further popularize the celebration.

5. THERE'S ANOTHER TALE ABOUT THE ORIGINS OF THE HOLIDAY.

A 1922 ad in the Cleveland Plain Dealer.
A 1922 ad in the Cleveland Plain Dealer.
Wikimedia Commons // Public Domain

According to Hallmark, Sweetest Day came about because a candy company employee named Herbert Kingston simply wanted to spread joy to others and "bring happiness to the lives of those who often were forgotten." But The Atlantic calls this happy little story a complete fabrication, so take it with a grain of salt.

6. HALLMARK WAS LATE TO THE PARTY.

A man mailing a letter in 1960s New York.
Keystone, Getty Images

Though it's often referred to as a "Hallmark Holiday," Hallmark didn't actually get in on those sweet Sweetest Day profits until the 1960s—nearly 50 years after it was founded.

7. MOST SWEETEST DAY CARDS ARE ROMANTICALLY INCLINED.

This front-page Sweetest Day cartoon was published in The Cleveland Plain Dealer on October 8, 1921.
This front-page Sweetest Day cartoon was published in The Cleveland Plain Dealer on October 8, 1921.
Digital scan courtesy of The Cleveland Public Library Microform Center, Wikimedia Commons // Public Domain

Despite the fact that Sweetest Day started as a way to hawk candy to the downtrodden, it's now just another Valentine's Day for many people. Hallmark makes more than 70 Sweetest Day cards—and 80 percent of them are romantic.

8. FOR SOME, IT'S MORE POPULAR THAN MOTHER'S DAY.

A little boy gives his mother some flowers
Hulton Archive, Getty Images

According to Retail Confectioners International, some retailers say their sales for Sweetest Day are better than their sales for Mother's Day. (Sorry, mom.)

9. THESE DAYS, SWEETEST DAY ISN'T JUST ABOUT THE CANDY.

Two women laughing together.
Fox Photos, Getty Images

Though those commemorating the holiday can certainly buy candy, that's just one of the ways people can express their appreciation for anyone who might not otherwise have a special day (a favorite aunt, a next-door neighbor, the pet sitter). Various ways to celebrate Sweetest Day include flowers, cards, gifts, or simply just doing good deeds for others.

10. NEVER HEARD OF SWEETEST DAY? YOU'RE NOT ALONE.

An ice cream vendor in New York hands a young girl an ice cream in the 1920s.
Elizabeth R. Hibbs, Hulton Archive/Getty Images

Sweetest Day never gained as much ground nationally as it did in the Great Lakes region. The main states that celebrate sweetness on the third Saturday of October are Illinois, Indiana, Michigan, Ohio, and Wisconsin, though it has also spread to areas of New York, Pennsylvania, Florida, Texas, and California. The biggest Sweetest Day cities are Detroit, Buffalo, and of course, Cleveland.

This story first ran in 2016.

Today is National Necktie Day in Croatia—Birthplace of the Necktie

Srdjan Stevanovic, Getty Images
Srdjan Stevanovic, Getty Images

If you're wearing a necktie to work today, you can thank (or blame) the Croatians for this stylish invention. The necktie's predecessor, a short knotted garment called the cravat, is a source of pride in this Western Balkan nation—so much so that they celebrate Cravat Day each year on October 18.

It's unclear when exactly the necktie was invented, but Croatian soldiers wore red cravats as part of their uniform during the Thirty Years' War (1618-1648). According to The Atlantic, Croatian mercenaries carried it to Western Europe that same century, and the French borrowed the idea and dubbed it the cravate. It became even more stylish when Louis XIV of France started wearing a lace cravat in 1646 at the tender age of 7, according to The Dubrovnik Times. The English eventually helped spread the accessory around the world, and it morphed into the elongated form we're most familiar with today.

In 1997, a nonprofit organization called the Academia Cravatica was founded to promote the cravat as a symbol of Croatian ingenuity. "By spreading the truth about the cravat, we improve Croatia's image in the international public," the organization states. "The fact that Croats invented the Cravat makes us proud to be Croats." (According to Time Out, Croatia also invented the first MP3 player, the zeppelin, the parachute, and fingerprint identification.)

The cravat is also tied up with national identity. The words Croat and cravat are etymologically linked, and were once different spellings of the same word. One sample sentence by David Hume in 1752 reads, "The troops are filled with Cravates and Tartars, Hussars, and Cossacs."

The holiday isn't normally a big to-do, but the county's capital city, Zagreb, occasionally gets pretty festive. In 2003, when the holiday first debuted in Croatia, the Academia Cravatica wrapped an oversized red necktie around Pula Arena, a Roman amphitheater. It took two years to prepare and five days to install—and at 2650 feet long, it ended up being the largest necktie in the world, as recognized by Guinness World Records.

Cravat Day was formally declared a holiday by Croatian Parliament in 2008, and it's been a hallmark of Croatian culture ever since. A few events were planned in Zagreb today, including a march featuring the "city's famous Cravat Regiment." So if you happen to be in the Croatian capital, now you know why more than 50 historic statues are looking dapper in their red cravats.

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