The original star-spangled banner which flew over Ft. McHenry. It is on display at the National Museum of American History. The area on the right which looks like a light blue puddle is where one of the stars is missing. (Barbara Haddock Taylor/Baltimore Sun)

Decades of careful restoration and study have revealed a lot about the flag that flew over Fort McHenry after its defenders fought off a naval attack during the War of 1812: the swatches taken as mementos of the pivotal battle, the areas worn by time, perhaps even sections damaged by British mortar fire.

But a gaping hole at the center of the original Star-Spangled Banner presents a question that no one has been able to answer: What happened to the missing star?

“It’s a major mystery,” said Lonn Taylor, a retired historian who helped the Smithsonian’s National Museum of American History reconstruct the story of the flag in the century after it left the fort and before it entered the museum’s collection.

The storied flag is getting increased attention as Baltimore and the country celebrate the 200th anniversary of the song that would become the national anthem. On Saturday the flag was to be displayed for the first time with Francis Scott Key’s original manuscript, on loan from the Maryland Historical Society.

For those who have studied the flag, the mystery of the missing star deepens its meaning. The answer may be found in how the banner’s legend grew along with that of Key’s verse. It was a war hero’s keepsake, a family heirloom, a military relic — and finally a revered symbol of national resilience.

“It tells a story,” said Suzanne Thomassen-Krauss, the textile conservator who maintains the flag at the museum in Washington. She believes somebody cut out the star for posterity in the 1800s. “It would be telling to know who got the star and why.”

There’s no hard evidence to explain what happened to the star. It’s not there in the first known photograph of the banner, taken in 1873 in Boston. Some believe it was given to President Abraham Lincoln during the Civil War; others have guessed that it went to Confederate President Jefferson Davis. It could have been destroyed.

Thomassen-Krauss thinks the star could just as likely be in the attic of someone who has no notion of its significance. That’s what happened with other pieces of the flag that have surfaced in recent years.

Only since the 1990s have historians gotten a firm grasp on the flag’s travels through the 1800s.

For most of that time, the banner was in possession of the descendants of George Armistead, commander at Fort McHenry during the bombardment on Sept. 13 and 14, 1814. It’s not clear whether it was given to the popular military leader or whether he took it on his own accord, but he left it to his family when he died in 1818.

Though the flag had personal significance to the Armistead family, its cultural meaning was less clear-cut until Key’s poem about the battle gained in popularity. Originally titled “Defence of Fort McHenry,” it was set to music, then took on added importance amid the patriotic sentiment of the Civil War.

The military began to use the song in ceremonies in the 1890s, and “The Star-Spangled Banner” became the national anthem in 1931.

In fact, the flag — originally 30 feet by 42 feet — is only the larger of two that historians believe flew during and after the bombardment. There is no official account of what happened to the smaller banner.

Over the decades, Armistead’s family allowed many people to cut off and keep fragments of the flag. Though it’s hard to believe today that anyone would alter such a historic object, those who have worked with the flag say it reflects the level of interest and pride in the flag during that era.

“I think it adds to the story,” said Amanda Shores Davis, executive director of The Star-Spangled Banner Flag House on East Pratt Street, the former home of Mary Pickersgill, who sewed the colors for Fort McHenry. (The museum has several pieces of the flag.) “It says something about this 19th-century culture of collection.”

In 1873, one of the Armisteads shipped the flag to Boston so it could be photographed by naval historian George Preble, who would do extensive research on it — and take several clippings of his own.

Several ensuing exhibitions increased the visibility and popularity of the flag, and the family would ultimately give it to the Smithsonian.

Because there are no photographs of the flag showing all of the stars, historians can only guess when the missing star was removed. The family only left one clue about what might have happened to it, as Georgiana Armistead Appleton wrote in 1873 that “the star was cut out for some official person.”

Henry T. Armistead, a retired Philadelphia-area librarian who is George Armistead’s great-great grandson, said he has no idea what happened to the star.

He feels a strong connection to his ancestry — he owns a historic Rembrandt Peale portrait of George Armistead — but does not know of anybody in the family with an account of the star.

“It looks horrible,” he said. “But it was part of the tradition, apparently.”

Some written accounts have reported that Lincoln might have been the recipient, but Taylor doubts that. Armistead family members who had the flag sympathized with the Confederacy during the Civil War, said Taylor, who has found no record in Lincoln’s papers of his receiving it.

Scott S. Sheads, a ranger at Fort McHenry who has done extensive research into the Battle of Baltimore, thinks the star might have been obliterated in the battle. A person who fought at the fort wrote that he had seen it take an explosive hit, Sheads said. (Other accounts say the flag was raised after the bombardment ended.)

“I can pretty much surely say that the star is missing because it was hit by a British mortar shell,” he said.

Thomassen-Krauss, the textile conservator, doesn’t believe that could be true.

There’s stitching around the hole where the star would have been, she said, adding that it’s unlikely anybody would have bothered with that so soon after the battle. Besides, she said, there’s a damaged area below the stars that might explain the account.

Unless the star is found, though, no one will know for sure. And the mystery will keep visitors to the Smithsonian guessing, wondering and imagining.

Davis said it’s natural for the bombardment to spring to mind when looking at the flag.

“It’s no wonder why we have this sort of … anecdotal history of bombs flying through the flag,” she said. “I’d love to get my hands on that star.”