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Autumn Equinox 2017: Today Is the First Day of Fall

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On September 22, at 4:02 p.m. ET, the Sun will shine directly over the equator—the midpoint of the Earth. 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.


An autumn equinox celebration at the Neris River waterfront in Vilnius, Lithuania.
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.
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.


Druids on London's Primrose Hill marking the autumn equinox.
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.

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15 Facts About the Summer Solstice
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It's the longest day of the year in the Northern Hemisphere, so soak up some of those direct sunrays (safely, of course) and celebrate the start of summer with these solstice facts.

1. THIS YEAR IT'S JUNE 21.

June 21 date against a yellow background
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The summer solstice always occurs between June 20 and June 22, but because the calendar doesn't exactly reflect the Earth's rotation, the precise time shifts slightly each year. For 2018, the sun will reach its greatest height in the sky for the Northern Hemisphere on June 21 at 6:07 a.m. Eastern Time.

2. THE SUN WILL BE DIRECTLY OVERHEAD AT THE TROPIC OF CANCER.

A vintage mapped globe showing the Tropic of Cancer
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While the entire Northern Hemisphere will see its longest day of the year on the summer solstice, the sun is only directly overhead at the Tropic of Cancer (23 degrees 27 minutes north latitude).

3. THE NAME COMES FROM THE FACT THAT THE SUN APPEARS TO STAND STILL.

Stonehenge at sunrise.
CARL DE SOUZA, AFP/Getty Images

The term "solstice" is derived from the Latin words sol (sun) and sistere (to stand still), because the sun's relative position in the sky at noon does not appear to change much during the solstice and its surrounding days. The rest of the year, the Earth's tilt on its axis—roughly 23.5 degrees—causes the sun's path in the sky to rise and fall from one day to the next.

4. THE WORLD'S BIGGEST BONFIRE WAS PART OF A SOLSTICE CELEBRATION.

A large bonfire
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Celebrations have been held in conjunction with the solstice in cultures around the world for hundreds of years. Among these is Sankthans, or "Midsummer," which is celebrated on June 24 in Scandinavian countries. In 2016, the people of Ålesund, Norway, set a world record for the tallest bonfire with their 155.5-foot celebratory bonfire.

5. THE HOT WEATHER FOLLOWS THE SUN BY A FEW WEEKS.

Colorful picture of the sun hitting ocean waves.
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You may wonder why, if the solstice is the longest day of the year—and thus gets the most sunlight—the temperature usually doesn't reach its annual peak until a month or two later. It's because water, which makes up most of the Earth's surface, has a high specific heat, meaning it takes a while to both heat up and cool down. Because of this, the Earth's temperature takes about six weeks to catch up to the sun.

6. THOUSANDS OF PEOPLE GATHER AT STONEHENGE TO CELEBRATE.

Rollo Maughfling, the Archdruid of Glastonbury and Stonehenge, conducts a Solstice celebration service for revelers as they wait for the midsummer sunrise at Stonehenge on June 21, 2012, near Salisbury, England.
Rollo Maughfling, the Archdruid of Glastonbury and Stonehenge, conducts a Solstice celebration service for revelers as they wait for the midsummer sunrise at Stonehenge on June 21, 2012, near Salisbury, England.
Matt Cardy, Getty Images

People have long believed that Stonehenge was the site of ancient druid solstice celebrations because of the way the sun lines up with the stones on the winter and summer solstices. While there's no proven connection between Celtic solstice celebrations and Stonehenge, these days, thousands of modern pagans gather at the landmark to watch the sunrise on the solstice.

7. PAGANS CELEBRATE THE SOLSTICE WITH SYMBOLS OF FIRE AND WATER.

Arty image of fire and water colliding.
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In Paganism and Wicca, Midsummer is celebrated with a festival known as Litha. In ancient Europe, the festival involved rolling giant wheels lit on fire into bodies of water to symbolize the balance between fire and water.

8. IN ANCIENT EGYPT, THE SOLSTICE HERALDED THE NEW YEAR.

Stars in the night sky.
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In Ancient Egypt, the summer solstice preceded the appearance of the Sirius star, which the Egyptians believed was responsible for the annual flooding of the Nile that they relied upon for agriculture. Because of this, the Egyptian calendar was set so that the start of the year coincided with the appearance of Sirius, just after the solstice.

9. THE ANCIENT CHINESE HONORED THE YIN ON THE SOLSTICE.

Yin and yang symbol on textured sand.
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In ancient China, the summer solstice was the yin to the winter solstice's yang—literally. Throughout the year, the Chinese believed, the powers of yin and yang waxed and waned in reverse proportion to each other. At the summer solstice, the influence of yang was at its height, but the celebration centered on the impending switch to yin. At the winter solstice, the opposite switch was honored.

10. IN ALASKA, THE SOLSTICE IS CELEBRATED WITH A MIDNIGHT BASEBALL GAME.

Silhouette of a baseball player.
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Each year on the summer solstice, the Alaska Goldpanners of Fairbanks celebrate their status as the most northerly baseball team on the planet with a game that starts at 10:00 p.m. and stretches well into the following morning—without the need for artificial light—known as the Midnight Sun Game. The tradition originated in 1906 and was taken over by the Goldpanners in their first year of existence, 1960.

11. THE EARTH IS ACTUALLY AT ITS FARTHEST FROM THE SUN DURING THE SOLSTICE.

The Earth tilted on its axis.
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You might think that because the solstice occurs in summer that it means the Earth is closest to the sun in its elliptical revolution. However, the Earth is actually closest to the sun when the Northern Hemisphere experiences winter and is farthest away during the summer solstice. The warmth of summer comes exclusively from the tilt of the Earth's axis, and not from how close it is to the sun at any given time. 

12. IRONICALLY, THE SOLSTICE MARKS A DARK TIME IN SCIENCE HISTORY.

Galileo working on a book.
Hulton Archive, Getty Images

Legend has it that it was on the summer solstice in 1633 that Galileo was forced to recant his declaration that the Earth revolves around the Sun; even with doing so, he still spent the rest of his life under house arrest.

13. AN ALTERNATIVE CALENDAR HAD AN EXTRA MONTH NAMED AFTER THE SOLSTICE.

Pages of a calendar
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In 1902, a British railway system employee named Moses B. Cotsworth attempted to institute a new calendar system that would standardize the months into even four-week segments. To do so, he needed to add an extra month to the year. The additional month was inserted between June and July and named Sol because the summer solstice would always fall during this time. Despite Cotsworth's traveling campaign to promote his new calendar, it failed to catch on.

14. IN ANCIENT GREECE, THE SOLSTICE FESTIVAL MARKED A TIME OF SOCIAL EQUALITY.

Ancient Greek sculpture in stone.
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The Greek festival of Kronia, which honored Cronus, the god of agriculture, coincided with the solstice. The festival was distinguished from other annual feasts and celebrations in that slaves and freemen participated in the festivities as equals.

15. ANCIENT ROME HONORED THE GODDESS VESTA ON THE SOLSTICE.

Roman statue of a vestal virgin
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In Rome, midsummer coincided with the festival of Vestalia, which honored Vesta, the Roman goddess who guarded virginity and was considered the patron of the domestic sphere. On the first day of this festival, married women were allowed to enter the temple of the Vestal virgins, from which they were barred the rest of the year.

A version of this list originally ran in 2015.

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12 Things You Might Not Know About Juneteenth
Wikimedia Commons // Public Domain
Wikimedia Commons // Public Domain

There's more than one Independence Day in the U.S. On June 19, 1865, General Gordon Granger rode into Galveston, Texas, and announced that slaves were now free. Since then, June 19 has been celebrated as Juneteenth across the nation. Here's what you should know about the historic event and celebration.

1. SLAVES HAD ALREADY BEEN EMANCIPATED—THEY JUST DIDN'T KNOW IT.

A page of the original Emancipation Proclamation on display from the National Archives.
A page of the original Emancipation Proclamation, from the National Archives.
ALEX WONG, AFP/Getty Images

The June 19 announcement came more than two and a half years after Abraham Lincoln issued the Emancipation Proclamation on January 1, 1863, so technically, from the Union's perspective, the 250,000 slaves in Texas were already free—but none of them were aware of it, and no one was in a rush to inform them.

2. THERE ARE MANY THEORIES AS TO WHY THE LAW WASN'T ENFORCED IN TEXAS.

Confederate General Robert E. Lee surrendering to Union General Ulysses S Grant at the close of the American Civil War, at the Appomattox Court House in Virginia on April 9, 1865.
Confederate General Robert E. Lee surrendering to Union General Ulysses S Grant at the close of the American Civil War, at the Appomattox Court House in Virginia on April 9, 1865.
Hulton Archive, Getty Images

News traveled slowly back in those days—it took Confederate soldiers in western Texas more than two months to hear that Robert E. Lee had surrendered at Appomattox. Still, some have struggled to explain the 30-month gap between the proclamation and freedom, leading some to suspect that Texan slave owners purposely suppressed the announcement. Other theories include that the original messenger was murdered to prevent the information from being relayed or that the Federal government purposely delayed the announcement to Texas in order to get one more cotton harvest out of the slaves. But the real reason is probably that Lincoln's proclamation simply wasn't enforceable in the rebel states before the end of the war.

3. THE ANNOUNCEMENT ACTUALLY URGED FREED SLAVES TO STAY WITH THEIR FORMER OWNERS.

Photograph portrait of Civil War General Gordon Granger
National Archives and Records Administration, Wikimedia Commons // Public Domain

General Order No. 3, as read by General Granger, said:

"The people of Texas are informed that, in accordance with a proclamation from the Executive of the United States, all slaves are free. This involves an absolute equality of personal rights and rights of property between former masters and slaves, and the connection heretofore existing between them becomes that between employer and hired labor. The freedmen are advised to remain quietly at their present homes and work for wages. They are informed that they will not be allowed to collect at military posts and that they will not be supported in idleness either there or elsewhere."

4. WHAT FOLLOWED WAS KNOWN AS "THE SCATTER."

Internet Archive Book Images, Flickr

Obviously, most former slaves weren't terribly interested in staying with the people who had enslaved them, even if pay was involved. In fact, some were leaving before Granger had finished making the announcement. What followed was called "the scatter," when droves of former slaves left the state to find family members or more welcoming accommodations in northern regions.

5. NOT ALL SLAVES WERE FREED INSTANTLY.

Illustration of a white man reading something to a black slave.
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Texas is a large state, and General Granger's order (and troops to enforce it) were slow to spread. According to historian James Smallwood, many enslavers deliberately suppressed the information until after the harvest, and some beyond that. In July 1867 there were two separate reports of slaves being freed, and one report of a Texas horse thief named Alex Simpson whose slaves were only freed after his hanging in 1868.

6. FREEDOM CREATED OTHER PROBLEMS.

Mist and fog over a river
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Despite the announcement, Texas slave owners weren't too eager to part with what they felt was their property. When legally freed slaves tried to leave, many of them were beaten, lynched, or murdered. "They would catch [freed slaves] swimming across [the] Sabine River and shoot them," a former slave named Susan Merritt recalled.

7. THERE WERE LIMITED OPTIONS FOR CELEBRATING.

A monument in Houston's Emancipation Park.
A monument in Houston's Emancipation Park.
2C2KPhotography, Flickr // CC BY 2.0

When freed slaves tried to celebrate the first anniversary of the announcement a year later, they were faced with a problem: Segregation laws were expanding rapidly, and there were no public places or parks they were permitted to use. So, in the 1870s, former slaves pooled together $800 and purchased 10 acres of land, which they deemed "Emancipation Park." It was the only public park and swimming pool in the Houston area that was open to African Americans until the 1950s.

8. JUNETEENTH CELEBRATIONS WANED FOR SEVERAL DECADES.

Scene from the Poor People's March in Washington, D.C. on June 19, 1968.
Scene from the Poor People's March in Washington, D.C. on June 19, 1968.
ARNOLD SACHS, AFP/Getty Images

It wasn't because people no longer wanted to celebrate freedom—but, as Slate so eloquently put it, "it's difficult to celebrate freedom when your life is defined by oppression on all sides." Juneteenth celebrations waned during the era of Jim Crow laws until the civil rights movement of the 1960s, when the Poor People's March planned by Martin Luther King Jr. was purposely scheduled to coincide with the date. The march brought Juneteenth back to the forefront, and when march participants took the celebrations back to their home states, the holiday was reborn.

9. TEXAS WAS THE FIRST STATE TO DECLARE JUNETEENTH A STATE HOLIDAY.

A statue of former Texas state representative Al Edwards, who introduced legislation to have June 19 officially declared a state holiday.
A statue of former Texas state representative Al Edwards, who introduced legislation to have June 19 officially declared a state holiday.
ניקולס, Flickr // CC BY-SA 2.0

Texas deemed the holiday worthy of statewide recognition in 1980, the first state to do so.

10. JUNETEENTH IS STILL NOT A FEDERAL HOLIDAY.

Silhouette of woman walking
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Though most states now officially recognize Juneteenth, it's still not a national holiday. As a senator, Barack Obama co-sponsored legislation to make Juneteenth a national holiday, though it didn't pass then or while he was president. One supporter of the idea is 91-year-old Opal Lee—since 2016, Lee has been walking from state to state to draw attention to the cause.

11. THE JUNETEENTH FLAG IS FULL OF SYMBOLISM.

a mock-up of the Juneteenth flag
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Juneteenth flag designer L.J. Graf packed lots of meaning into her design. The colors red, white, and blue echo the American flag to symbolize that the slaves and their descendants were Americans. The star in the middle pays homage to Texas, while the bursting "new star" on the "horizon" of the red and blue fields represents a new freedom and a new people.

12. JUNETEENTH TRADITIONS VARY ACROSS THE U.S.

Juneteenth celebration participants taste the sweet potato pie entered in the cook-off contest during the festivities Richmond, California, in 2004.
Juneteenth celebration participants taste the sweet potato pie entered in the cook-off contest during the festivities Richmond, California, in 2004.
David Paul Morris, Getty Images

As the tradition of Juneteenth spread across the U.S., different localities put different spins on celebrations. In southern states, the holiday is traditionally celebrated with oral histories and readings, "red soda water" or strawberry soda, and barbecues. Some states serve up Marcus Garvey salad with red, green, and black beans, in honor of the black nationalist. Rodeos have become part of the tradition in the southwest, while contests, concerts, and parades are a common theme across the country.

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