The Tribute in Light illuminates the sky over New York's lower Manhattan skyline a day ahead of the 11-year anniversary of the 9/11 attacks, Monday (Photo: Reuters)
Americans mark the 11th anniversary of the September 11 attacks on Tuesday with relatively low-key ceremonies that reflect a gradual dampening of passions around the fateful day.
The main event will be a ritual reading at New York's Ground Zero of the names of the 2,983 people killed both on 9/11 and in the precursor to those attacks, the 1993 car bombing of the World Trade Center.
Relatives of the dead will take turns to read the names against a backdrop of mournful music.
They will pause for moments of silence marking the time when each of the four planes hijacked by Al-Qaeda turned into fireballs – two smashing into the Twin Towers, one into the Pentagon and one into a Pennsylvania field.
Another two moments of silence will be observed at the times the two towers collapsed, accounting for the vast majority of 9/11's victims.
However, this year New York Mayor Michael Bloomberg and other politicians will not take the podium at Ground Zero, in contrast with last year's 10th anniversary, when President Barack Obama led a long list of VIP guests.
Obama and his wife Michelle will observe the anniversary with a moment of silence outside the White House, then visit the Pentagon memorial.
Vice President Joe Biden, meanwhile, will travel to Shanksville, Pennsylvania, where United flight 93 crashed after passengers attacked the hijackers and thwarted a worse disaster.
The White House said Obama had been briefed by "key national security principals on... preparedness and security posture" for the anniversary.
But in keeping with the lower key atmosphere this year, there will apparently be no official suspension of the bitter presidential campaign.
Former president Bill Clinton will be campaigning for Obama and speaking out against Republican Mitt Romney at an event in Miami.
The passage of time appears to have cooled public attention to September 11, particularly after the huge media coverage of the 10th anniversary, which many saw as a suitable moment for allowing commemorations to peak.
A skyscraper at One World Trade Center is near completion and is again the tallest building in New York, as were the Twin Towers before they came down.
The killing by American troops of al-Qaeda founder Osama bin Laden in May 2011 has helped draw a line under 9/11, as has the opening of the Ground Zero memorial, where last year's ceremonies were held.
Bin Laden's successor Ayman al-Zawahiri released a video on the eve of this year's anniversary in which he confirmed that his deputy, Abu Yayha al-Libi, had been killed in a drone strike in Pakistan in June.
Libi was considered Al-Qaeda's global propaganda mastermind and his death dealt the biggest blow to the group since the killing of bin Laden.
This year sees the publishing on Tuesday of a book by a former US Navy SEAL who was among the troops who shot dead bin Laden in his Pakistan hideout.
The book describes in gory detail how the special forces killed the fugitive, then radioed back the news, saying it was "for God and country."
The Pentagon has threatened legal action against the author, who uses the penname Mark Owen but has been outed by the US media as Matt Bissonnette.
Last week, Obama said in a radio address that the United States is "stronger, safer and more respected in the world" since 9/11.
But his Republican opponent has accused Obama of weak leadership during the Arab Spring turmoil and of failing to be tough enough on Iran's government.
In Afghanistan, which once hosted bin Laden, US troops continue to battle the Taliban, Islamist fighters who were driven from power during the invasion a decade ago but have since regrouped.
Most foreign troops are scheduled to withdraw by the end of 2014, handing over responsibility for combat to Western-backed Afghan government forces.