PHILADELPHIA — America celebrated its 227th birthday by opening a new museum for the Constitution in its birthplace, marking the centennial of aviation and giving a red-white-and-blue welcome to troops returning home to Kansas from Iraq.

In Dayton, Ohio, President Bush climbed a flag-draped stage flanked by military jets to praise the work of U.S. troops and celebrate the 100th anniversary of flight in the hometown of the Wright brothers.

"Today and every day, the people of this land are grateful for their freedom, and we are proud to call ourselves citizens of the United States of America," Bush told a cheering crowd on a tarmac at Wright-Patterson Air Force Base.

Natalie Neal, 39, of nearby West Chester, Ohio, was up before dawn to secure a place in the crowd of thousands.

"There's not a better way to spend the Fourth of July than with your military and with your president," Neal said.

At Forbes Field in Topeka, Kan., parents, spouses and children of 135 National Guard soldiers found one better way to celebrate: hugging their loved ones for the first time since the soldiers left for Iraq five months ago.

"I'm not sure that any of us really appreciates the struggles George Washington went through in Valley Forge. This kind of personalizes those sacrifices," said Bill Burkett of Muskogee, Okla., whose daughter was among the returning troops. Other troops were returning home Friday to North Carolina, Wisconsin and Maine.

Anecita Hudson, whose son was a POW in Iraq, began celebrating the holiday Wednesday at Fort Bliss, Texas, where Army Spc. Joseph Hudson and other former POWs receive medals for bravery. The Hudsons were back in their hometown of Alamogordo, N.M., for the Fourth of July.

"It's really kind of overwhelming to see them all celebrating," Anecita Hudson said.

Chicago got a jump on the holiday, shooting off its fireworks extravaganza Thursday night to the "1812 Overture" before a crowd of 1.15 million people at the edge of Lake Michigan.

In the nation's birthplace, Philadelphia leaders honored the first female Supreme Court justice, Sandra Day O'Connor, with the city's Liberty Medal for embodying the founding principles of the nation.

O'Connor also joined jazzman Wynton Marsalis, Pennsylvania Gov. Ed Rendell and others in opening the new National Constitution Center.

The duty to uphold the Constitution is shared by citizens, lawmakers, presidents and judges alike, O'Connor told a crowd outside the new museum, about three blocks from Independence Hall, where the Constitution was drafted in 1787.

"I find the system quite comforting," O'Connor said. "By spreading the responsibility to uphold the Constitution among so many, the framers enlisted a legion of defenders for their new charter."

The new $185 million center holds the first public printings of the Constitution, an inkwell Abraham Lincoln used in signing the Emancipation Proclamation and exhibits recalling the many controversies that have tested the Constitution in its history, including tickets to President Andrew Johnson's 1868 impeachment trial and a lock pick from the Watergate burglary.

O'Connor and the other celebrities got a scare during the ceremony when a heavy frame crashed onto the stage as they pulled ribbons to reveal a mural. Three people, including Philadelphia's mayor and the museum's president, were treated for minor injuries.

Security was lighter in many cities compared to last year, when the Sept. 11 terrorist attacks were fresh in many minds.

Baltimore raised its alert status Thursday to its second highest level, mostly as a practice run, officials said, while the federal terror alert status remained unchanged at yellow, the middle of the five-color scale.

In Dearborn, Mich., home to one of the nation's largest concentrations of people with roots in the Middle East, turmoil overseas heightened the importance of this Independence Day for many.

"Independence," said Shane Safawi, who emigrated from Lebanon in 1988 and became a U.S. citizen about five years later. "The word itself means a lot. You are free. The whole country is free. It is a moment that you celebrate."