By Curt Anderson, Associated Press

Math enthusiasts around the world, from college kids to rocket scientists, celebrate Pi Day on Thursday, which is March 14 or 3/14 — the first three digits of an infinite number with many practical uses.

Around the world many people will mark the day with a slice of pie — sweet, savory or even pizza.

Manager Stephen Jarrett prepares pies on a counter at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

Simply put, pi is a mathematical constant that expresses the ratio of a circle’s circumference to its diameter. It is part of many formulas used in physics, astronomy, engineering and other fields, dating back thousands of years to ancient Egypt, Babylon and China.

Pi Day itself dates to 1988, when physicist Larry Shaw began celebrations at the Exploratorium science museum in San Francisco. The holiday didn’t really gain national recognition though until two decades later. In 2009, Congress designated every March 14 to be the big day — to hopefully spur more interest in math and science. Fittingly enough, the day is also Albert Einstein’s birthday.

Here’s a little more about the holiday’s origin and how it’s celebrated today.

WHAT IS PI?

Pi can calculate the circumference of a circle by measuring the diameter — the distance straight across the circle’s middle — and multiplying that by the 3.14-plus number.

Employees work a busy bakery kitchen at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

It is considered a constant number and it is also infinite, meaning it is mathematically irrational. Long before computers, historic scientists such as Isaac Newton spent many hours calculating decimal places by hand. Today, using sophisticated computers, researchers have come up with trillions of digits for pi, but there is no end.

WHY IS IT CALLED PI?

It wasn’t given its name until 1706, when Welsh mathematician William Jones began using the Greek symbol for the number.

Manager Stephen Jarrett prepares pies on a counter in a busy bakery kitchen at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

Why that letter? It’s the first Greek letter in the words “periphery” and “perimeter,” and pi is the ratio of a circle’s periphery — or circumference — to its diameter.

WHAT ARE SOME PRACTICAL USES?

The number is key to accurately pointing an antenna toward a satellite. It helps figure out everything from the size of a massive cylinder needed in refinery equipment to the size of paper rolls used in printers.

A freshly sliced piece of chicken pot pie is plated on a counter at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

Pi is also useful in determining the necessary scale of a tank that serves heating and air conditioning systems in buildings of various sizes.

NASA uses pi on a daily basis. It’s key to calculating orbits, the positions of planets and other celestial bodies, elements of rocket propulsion, spacecraft communication and even the correct deployment of parachutes when a vehicle splashes down on Earth or lands on Mars.

Using just nine digits of pi, scientists say it can calculate the Earth’s circumference so accurately it only errs by about a quarter of an inch (0.6 centimeters) for every 25,000 miles (about 40,000 kilometers).

IT’S NOT JUST MATH, THOUGH

Every year the San Francisco museum that coined the holiday organizes events, including a parade around a circular plaque, called the Pi Shrine, 3.14 times — and then, of course, festivities with lots of pie.

A country apple pie is sliced at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

Around the country, many events now take place on college campuses. For example, Nova Southeastern University in Florida will hold a series of activities, including a game called “Mental Math Bingo” and event with free pizza (pies) — and for dessert, the requisite pie.

“Every year Pi Day provides us with a way to celebrate math, have some fun and recognize how important math is in all our lives,” said Jason Gershman, chair of NSU’s math department.

At Michele’s Pies in Norwalk, Connecticut, manager Stephen Jarrett said it’s one of their biggest days of the year.

Manager Stephen Jarrett prepares pies on a counter at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

“We have hundreds of pies going out for orders (Thursday) to companies, schools and just individuals,” Jarrett said in an interview. “Pi Day is such a fun, silly holiday because it’s a mathematical number that people love to turn into something fun and something delicious. So people celebrate Pi Day with sweet pies, savory pies, and it’s just an excuse for a little treat.”

NASA has its annual “Pi Day Challenge” online, offering people plenty of games and puzzles, some of them directly from the space agency’s own playbook such as calculating the orbit of an asteroid or the distance a moon rover would need to travel each day to survey a certain lunar area.

WHAT ABOUT EINSTEIN?

Possibly the world’s best-known scientist, Einstein was born on March 14, 1879, in Germany. The infinite number of pi was used in many of his breakthrough theories and now Pi Day gives the world another reason to celebrate his achievements.

A freshly decorated chocolate peanut butter pie rests on a counter at Michele’s Pies, Wednesday, March 13, 2024, in Norwalk, Conn. Math enthusiasts and bakers celebrate Pi Day on March 14 or 3/14, the first three digits of a mathematical constant with many practical uses. Around the world many people will mark the day with a slice of sweet or savory pie. (AP Photo/John Minchillo)

In a bit of math symmetry, famed physicist Stephen Hawking died on March 14, 2018, at age 76. Still, pi is not a perfect number. He once had this to say:

“One of the basic rules of the universe is that nothing is perfect. Perfection simply doesn’t exist. Without imperfection, neither you nor I would exist.”

Associated Press video journalist John Minchillo contributed from Norwalk, Connecticut.

By Julia Frankel, Associated Press

JERUSALEM (AP) — A brother contemplated suicide. A sister stopped going to school. A father barely speaks. With each passing day, the relatives of hostages held in Gaza since Oct. 7 face a deepening despair.

Their hopes were raised that a cease-fire deal was near to bring some of their loved ones home by the start of Ramadan, the Muslim holy month that began Monday. But that informal deadline passed without any agreement.

Israeli Prime Minister Benjamin Netanyahu’s promise of “total victory” in the war against Hamas now rings hollow for many hostages’ families after five emotionally draining months.

“We are reading the news every single minute. Egypt says something, the Qataris say something different, the Americans say a deal is close, Israel says it’s not,” said Sharon Kalderon, whose brother-in-law, Ofer, remains in captivity. “We try to read between the lines, but we haven’t heard anything about Ofer for months. Nothing that can help us breathe.”

A demonstrator wrapped in the Israeli flag holds a sign during a rally calling for the release of the hostages held in the Gaza Strip by Hamas, in Tel Aviv, Israel, Saturday, March 9, 2024. (AP Photo/Ariel Schalit)

When Hamas-led fighters stormed into southern Israel on Oct. 7, they killed some 1,200 people, mostly civilians, and took around 250 hostages. Since then, Israel’s offensive has killed more than 31,000 Palestinians, according to Gaza health officials, and driven hundreds of thousands to the brink of starvation.

Hamas has been designated as a terrorist organization by the United States, Canada and the European Union.

About 120 hostages were freed during a November cease-fire that also led to the release of hundreds of Palestinians from Israeli prisons; three hostages were accidentally killed by Israeli forces during an attempted rescue mission. Now families are focused on bringing home the remaining hostages, at least 34 of whom are dead, according to the Israeli government.

Some families channel their desperation into unrelenting advocacy — traveling to the U.N. in New York, marching to Jerusalem from southern Israel, or wearing red shirts emblazoned with the words “Bring them Home” while running the Jerusalem marathon.

Friends and relatives of the Israeli hostages held in the Gaza Strip by Hamas attend a rally calling for their release, in Tel Aviv, Israel, Saturday, March 9, 2024. (AP Photo/Ariel Schalit)

But for other families, a quieter suffering has taken hold.

“You see some of the families running around, going on the TV, making noise. These are the ones that are holding on,” said Ricardo Grichener, the uncle of Omer Wenkert, a 22-year-old hostage. “The ones that are not leaving the houses, they are in a really bad situation.”

Since their home in Kibbutz Nir Oz was destroyed Oct. 7, Sharon Kalderon and her husband, Nissan, have stayed on the 12th floor of an apartment building in the Israeli city of Ramat Gan. Ofer, Nissan’s only brother, remains in captivity.

Nissan said he’s recently thought about killing himself.

“This situation is hard. I don’t sleep, I don’t eat. Not working. Nothing. I lose my mind. That’s all. It’s too much,” said Nissan.

“Whenever he goes out to the balcony, I get scared,” Sharon said.

International mediators had been optimistic they could broker a pre-Ramadan deal by bundling a six-week cease-fire with the release of dozens of Israeli hostages and Palestinian prisoners, and the entry of a large amount of humanitarian aid into Gaza. But Hamas wanted assurances of a longer-term end to the fighting, which Israel refused.

“We don’t see a prospect for a deal unless (U.S. President Joe) Biden does a miracle. We don’t see any way out. We don’t see any reason why Hamas would be flexible. They gain nothing,” said Grichener. “We are pressing the (Israeli) government, but I think their mistakes have already been made.”

Friends and relatives of the Israeli hostages held in the Gaza Strip by Hamas attend a rally calling for their release, in Tel Aviv, Israel, Saturday, March 9, 2024. (AP Photo/Ariel Schalit)

His nephew in captivity, Omer, needs medication to treat his digestive disease. His family doubts the medical aid for hostages that entered Gaza in January ever made it to him.

Meetings between the families and war cabinet officials are ongoing, but families feel powerless to change the sweep of negotiations. Many have received no official updates on the status of their loved ones, clinging instead to snippets conveyed by hostages released in November.

Shlomi Berger, the father of 19-year-old Agam Berger, said he last heard that she was alive in November. A hostage released during the cease-fire, Agam Goldstein-Almog, told him that his daughter — one of 19 women hostages, according to Israel — was alive and had wished him a happy birthday.

“You can imagine what it was like to get a sign of life from my daughter for the first time,” said Berger.

Police use a water cannon to disperse demonstrators protesting against Israeli Prime Minister Benjamin Netanyahu’s government, and calling for the release of hostages held in the Gaza Strip by Hamas, in Tel Aviv, Israel, Saturday, March 9, 2024. (AP Photo/Ariel Schalit)

But months later that excitement is tempered by considerable anxiety and uncertainty — and by some former hostages’ accounts of harrowing conditions.

“Nobody knows her situation. If she has air, if she has water, if she has bandages for her period. It’s crazy. I don’t know if somebody has sexually abused her.” said Berger. “We don’t know if she’s alive or dead. We just don’t know.”

Israel’s National Insurance pays for mental health counseling for parents, spouses, and children of hostages. Still, the situation has paralyzed Berger’s family.

One of his three daughters, a senior in high school, has not gone to school since Oct. 7. One of his young daughters has stopped eating. His wife, an industrial engineer, does not go to work. He tries to avoid the news, to save himself the daily roller coaster.

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“One minute you read the news and say, okay, it’s close, and another minute it’s not. Nobody really knows what’s happening,” he said.

Overnight, the parents of 33-year-old Or Levy became caretakers to Levy’s 2-year-old son, Almog. Hamas fighters killed Almog’s mother, Eynav, and took Levy hostage on Oct. 7. The family had to explain to young Almog that his mother is dead and his father missing.

“Most days I don’t even recognize my parents. My dad barely talks. Before Oct. 7, the last thing you could say about him was that he was a fragile man and now everybody who sees him is afraid to hug him,” said Michael Levy, Or’s brother. Levy said he’s lost 9 kilos (20 pounds) and barely sleeps.

Going forward, relatives said their strategies won’t change. They will continue to meet with the war cabinet, continue hoping for an eventual release.

On Monday, Sharon and Nissan Kalderon watched the sun set on the first full day of Ramadan.

“We really thought, today is the day,” Sharon said. “But unfortunately, this is just another day.”