Other readers, who were older and in the military at the time, remembered being hastily ordered to scramble, the possibility of war with Russia suddenly seeming imminent. And people who had worked in offices recalled clutching colleagues while watching revered newscaster Walter Cronkite remove his glasses on television when Kennedy was pronounced dead in Dallas, because he needed a moment before he could go on.
Numerous readers wrote that the murder "ended our innocence." Few events came close in intensity, they said.
"The news hit like a left hook out of nowhere," Barry Springel of Yardley wrote.
The sentiment was echoed by Evelyn Allen-Chase of Elkins Park: "I never felt as sad and afraid as I did that day - until Sept. 11."
Kennedy was shot at 12:30 p.m. Central Standard Time, 1:30 p.m. here.
In the Philadelphia area, young people were in school, and were alerted to the assassination by school personnel.
"Sister Clementine . . . [was] unarguably the toughest nun in school," wrote Frank DiPinto of Sewell, Gloucester County, who had attended Our Lady of Pompeii in North Philadelphia. Nonetheless, he said, after the mother superior had imparted the news, Sister Clementine's "tears projected forward and the moist droplets streaked the dusty chalk marks [on the blackboard] into gray sweeping streaks. Sister then turned and collapsed at her desk, sobbing."
At St. Peter's School in Riverside, Burlington County, Joe Catanzariti wrote, the students were told: "Please suspend what you are doing and pray for the president."
In an odd moment embedded five decades into Robert Saettler's memory, an English teacher at Wildwood High School relayed the news this way: "Attention, class: President Kennedy has been shot and will probably die. Now finish your tests."
Saettler said the teacher then sat down at her desk and resumed reading a novel.
When children got home, the mood darkened.
"My big, strong, tough, Irish Catholic longshoreman father had tears in his eyes," wrote George Badey III, of Fitler Square. "That's when it hit me. This was really bad."
It's what Evangeline Rush DiCastanado from Eastwick concluded: "That day, I discovered a horrible new expression on the faces of my family and friends. . . . I was an adult before I could name that expression. It was stunned disbelief."
John Rooney of Merion Station said that the face he remembered belonged to his grandfather - "the vacant look, like someone had taken something very special away from him. That something was hope for the future."
In an interview, Rooney, 58, an IT executive in Devon, said that on Sept. 11 he immediately thought of the Kennedy assassination and decided to give blood, as a gesture to support America.
Both days shook him, he said, adding, "With JFK, his death made us realize we weren't as safe as we thought, and that evil was getting into our psyche.
"By 9-11, the devil had arrived. He was here."
What helped make the JFK assassination so memorable was television.
The assassination itself was not immediately seen - the Zapruder film that depicted the shooting was not available yet.
But news coverage after the assassination was nonstop, with no programs or commercials broadcast, unprecedented in the then-short history of the medium, according to Barbie Zelizer, communication professor at the Annenberg School for Communication at the University of Pennsylvania.
Then on Sunday, as though looking through the same window at the same time, the country watched in disbelief as Jack Ruby shot and killed JFK's assassin, Lee Harvey Oswald, a troubled 24-year-old former Marine sharpshooter with ties to Moscow.
"We got home from church . . . just in time to see Oswald gunned down, the first and last reality show I've seen," wrote Kenneth Foti of Malvern.
The story continued, through "the longest weekend in the 20th century in America," according to Jim Hilty, history professor emeritus at Temple University. "We stopped as a society until Kennedy was in his grave Monday."
And television recorded all of it - Jacqueline Kennedy's bloodstained dress, the riderless horse in the funeral cortege, John F. Kennedy Jr. saluting his father's casket.
"This was the first time that TV news played a role in people's lives," Zelizer said. "The images made a community out of grieving, bereft, frightened people. TV created a go-to place that people could gather around."
At Denise Rolfe's house in Huntingdon Valley, "our massive Philco . . . with rabbit ears . . . stayed on throughout the weekend . . . previously unheard of in our house. Walter Cronkite . . . [became] the extra family member we trusted for our live connection to a different, non-Camelot reality."
The theme of the disintegration of Camelot - the JFK era of hope and good feeling - recurred throughout reader responses.
"Things never seemed the same after that day," wrote Bill Milligan of Clementon.
"It was . . . the weekend that I stopped being a naive teenager and realized that bad things can happen to good people," wrote Bill Godfrey of Woodstown, Salem County. "I stopped looking . . . through rose-colored glasses."
It's not as though all was well in America before the assassination.
The civil rights movement had been an endless series of shocks, said Temple history professor David Farber.
Two months before Kennedy was killed, a bomb planted at the 16th Street Baptist Church in Birmingham, Ala., had killed four African American girls.
And the Cuban missile crisis a year before the assassination briefly confronted Americans with the possibility that life could be blinked out within seconds in a world laden with nuclear weapons.
Still, the youthful Kennedy with his beautiful wife and children represented something golden and fine in Americans' eyes, Farber said. And the end of World War II had created a victory culture in the United States, a sense of American invincibility, he said.
But Kennedy's sudden, awful death symbolized the collapse of possibility for so many.
For baby boomers growing up safe in the suburbs, the assassination stripped away feelings of stability, said Mark Siegert, a Millburn, Essex County, psychologist and an expert on the effects of traumatic events.
"People saw their parents shaken, and that's where their sense of security is shaken," Siegert said. "It can affect you for the rest of your life. It's not as bad as seeing your parents murdered. But your sense of safety is never the same anymore."
The fear that the universe was hopelessly askew was at the heart of the question then-fifth grader John Gillian of Stratford, Camden County, posed to his mother after he later saw the splotches on the first lady's suit:
"Mommy, is everything going to be all right?"
Gillian remembered his mother looking at him and responding: "I don't know."
Away from home, people from this region who were in the military on the day Kennedy was killed experienced eerie and disorienting hours.
Members of the U.S. armed forces were put on full alert stateside and on America's many bases overseas, including Spain, Turkey, Italy, and Germany.
Dominic Grady of Coatesville was dancing with his wife at the officers club in Augsburg, Germany, "when the music suddenly stopped. Someone at the microphone said, 'The president has been shot. All personnel return to your units immediately.'
"It was a surreal moment," he wrote, adding that everyone was ordered to "assembly areas in the German woods not knowing whether we would ever see our families again."
At Sheppard Air Force Base in Wichita Falls, Texas, 19-year-old Thomas Seidner of Havertown had a cold. He was walking toward the base hospital for medicine when he felt the ground shake soon after the assassination.
In an interview, Seidner recalled that 25 B-52 bombers had instantly switched on. With eight engines per aircraft, the noise was cacophonous, as black smoke rose from the vibrating planes.
"They began taking off every 30 seconds," Seidner, a former AT&T project manager, said. "I didn't know what we were heading to. I'll remember this forever."
William Smeck, a resident of Springfield, Delaware County, was aboard the troop-transport ship USNS William O. Darby on the way to Germany when he learned of the assassination. He recalled that not everyone was crestfallen over the news.
It was "almost 6:45 p.m. when the ship's Captain made the late announcement: We have just received a message saying President Kennedy has been shot in Dallas, Texas. At this time we do not have any additional information," Smeck e-mailed The Inquirer. He continued:
"Just then one guy cheered, 'Yeaaaa!!'
"The idiot's cheer was cut short by a very curt and forceful retort, 'Shut up! The President's just been shot. This ain't some game!' "
Life changed after JFK's murder, hundreds of readers wrote.
Many saw the assassination as the beginning of a slide toward chaos, and the emergence of a diminished, tarnished America: the escalation of the Vietnam War; the killings of Malcolm X, Martin Luther King Jr., and Robert Kennedy; riots in major cities; Watergate. The high hopes of the Kennedy years morphed into more cynical times.
"One, maybe two bullets changed the world, and we have surely never been the same since," wrote Stuart Morris of Collegeville.
Historians see it differently.
"Nothing bad happened to the country directly because of the assassination," Farber said.
In fact, some things improved.
When Kennedy's vice president, Lyndon Johnson, became president, he invoked Kennedy's legacy to pass landmark civil rights legislation, to institute a war on poverty, and to create Medicare, Farber said.
"The American fabric remained strong," he said.
While trauma can be damaging, it can also help, said psychologist Lawrence Calhoun from the University of North Carolina, Charlotte.
So-called post-traumatic growth actually encourages people to reach out to others after a stressful event to connect, Calhoun said. "It also gives you greater appreciation for what you have."
Still, many believe, "we'd be better off if JFK and Bobby and King had lived," Hilty said.
Readers repeated this idea, imbuing Kennedy with a kind of magic that somehow would have ameliorated America.
"We all had hopes and dreams that were shattered on that day," wrote Carol DeBunda of Abington. "Fifty years have passed and we are still looking to find understanding that leads to . . . a more peaceful society."
Dissatisfied with life, re-traumatized by Sept. 11, and still unable to understand why Kennedy was killed and what really happened that day in Dallas even after 50 years, many readers expressed endless questions.
In the end, however, it's clear that readers who were children when Kennedy was killed have grown up, and learned a thing or two.
"How could anyone go on doing normal things after such a monumental event?" asked Terri Ely of Bridgeton, Salem County. "But I found, as my parents did before me, that life goes on.
"Our country survives."
Read hundreds of readers' personal recollections of the day President Kennedy died at www.inquirer.com/KennedyRemembered