DALLAS — For a moment Friday, it was as if time had stopped.
Fifty years to the minute after President John F. Kennedy was shot to death while his motorcade passed through Dealey Plaza — as gray skies loomed overhead and drizzle steadily fell — thousands of people gathered at that very spot fell silent.
Some bowed their heads.
Others tilted heads back, eyes closed, heavenward.
And some cautiously turned their eyes toward the Texas School Book Depository, where government officials have said the shots came from years ago.
Then, church bells tolled.
“A new era dawned and another waned half a century ago, when hope and hatred collided right here in Dallas,” Dallas Mayor Mike Rawlings said of the assassination that threw Dallas under national scrutiny — and negativity — for decades. “In our front yard, our president had been taken from us.
“It seems that we all grew up that day,” he said. “Our collective hearts were broken.”
Somber remembrances extended from Dallas to Cape Cod’s shores, with moments of silence, speeches by historians, and, simple reverence for a time and a leader long gone.
“We watched the nightmarish reality in our front yard,” Mr. Rawlings told the crowd, which assembled just steps from the book depository where Lee Harvey Oswald fired from the sixth floor at Mr. Kennedy’s open-top limousine. “Our president had been taken from us, taken from his family, taken from the world.”
Two generations later, the assassination stirs quiet sadness in Baby Boomers who remember it as the start of a darker, more cynical time.
Historian David McCullough said Mr. Kennedy “spoke to us in that now-distant time past, with a vitality and sense of purpose such as we had never heard before.”
Mr. Kennedy “was young to be president, but it didn’t seem so if you were younger still,” Mr. McCullough added. “He was ambitious to make it a better world, and so were we.”
Past anniversaries in Dealey Plaza have been marked mostly by loose gatherings of the curious and conspiracy-minded, featuring everything from makeshift memorials and marching drummers to freewheeling discussions about others who might have been in on the killing.
Friday, the mayor unveiled a plaque with remarks the president was supposed to deliver that day in Dallas.
Drew Carney and his girlfriend, Chelsea Medwechuk, traveled from Toronto to attend the ceremony. Like many of those in attendance, they wore plastic ponchos to ward off the rain.
At 25 and 24, respectively, they were born a quarter-century after Mr. Kennedy died. Mr. Carney, a high school history teacher, said he became intrigued with Mr. Kennedy and his ideals as a teen.
“It filled you with such hope,” he said.
Elsewhere, flags were lowered to half staff and wreaths were laid at Mr. Kennedy’s presidential library and at a waterfront memorial near the family’s Cape Cod compound.
Attorney General Eric Holder paid his respects at Mr. Kennedy’s recently refurbished grave at Arlington National Cemetery, where a British cavalry officer stood guard, bagpipes played, and a flame burned steadily as it has since Mr. Kennedy was buried.
About an hour later, Jean Kennedy Smith, 85, the last surviving Kennedy sibling, laid a wreath at the grave, joined by about 10 members of the Kennedy family. They clasped hands for a short, silent prayer and left roses as a few hundred onlookers watched.
In Boston, Gov. Deval Patrick and Maj. Gen. Scott Rice of the Massachusetts National Guard endured a heavy rain during a wreath-laying ceremony at the Kennedy statue on the Statehouse front lawn. The statue, dedicated in 1990, has been largely off-limits since the 9/11 terrorist attacks. But the area was opened to visitors Friday.
Both of Mr. Kennedy’s grandfathers served in the Massachusetts Legislature, and in January, 1961, the president-elect came to the Statehouse to deliver one of his most famous addresses, known as the “City on a Hill” speech, just before leaving for his inauguration in Washington.
The tributes extended across the Atlantic to Ireland. In Dublin, Irish soldiers formed an honor guard outside the U.S. Embassy as the U.S. flag was lowered to half staff. An Irish army commander drew a sword and held it aloft as a lone trumpeter played “The Last Post,” the traditional British salute to war dead.
More than a dozen retired Irish army officers who, as cadets, had formed an honor guard at Mr. Kennedy’s graveside, gathered in the Embassy’s front garden to remember the first Irish-American to become leader of the free world.