The people came early to the Astrodome Saturday morning, thousands of them roaming the building once dubbed the Eighth Wonder of the World. They came to plunk down $200 for a pair of grandstand chairs, or to buy a swatch of honest-to-goodness Astroturf, or any of a raft of trinkets assembled across 48 years. Ninety minutes into this massive air-conditioned yard sale, Dinn Mann is on the telephone, trying to describe the exuberance all around him, the enthusiasm, the joy, the fellowship. “It’s the Game 7 we never got against the Mets back in ’86,” Mann says, laughing. “Mike Scott is on the mound today.” Today Mann, 48, is the executive vice president for MLB’s advanced media, and from his Manhattan office he has had a first-hand view of the revitalization of Hell’s Kitchen, has seen with great interest how the High Line has helped transform the Lower West Side, existing places given new leases on life with new ideas. On April 9, 1965, he was a month-old infant confined to an incubator when his mother, Dene, and his grandfather, Judge Roy Hofheinz, joined Gov. John Connally, President Lyndon Johnson and 47,879 to watch the Astros and Yankees open the Astrodome with an exhibition game, a 2-1 win for the Bombers, highlighted by a Mickey Mantle home run. The germ of the idea that would one day yield this splendid showcase had been born years earlier when Dene and the Judge had lamented once too often the number of times foul weather had called off a Houston Buffs baseball game. Hofheinz was already a larger-than-life only-in-America character who had been a state representative at 22, a county judge at 24, and mayor of Houston at 41. Now he would lead the effort to bring major league baseball to his city. And with it, the Dome. “People who aren’t from Houston don’t understand — probably can’t understand — that to us, this is more than just a stadium,” says Mann, who mirrored his grandfather’s precocious path, sports editor of his hometown Houston Post before age 30, and at the Kansas City Star by 31 before joining MLB in 2009. “This is our Golden Gate Bridge, our Empire State Building.” And for Mann, of course, it was something even more: It was his grandfather’s house, his own summer residence, his own backyard. One of the items he saw on sale Saturday struck him to his core: vintage astronaut helmets once worn by the Astrodome grounds crew. And suddenly he was 5 years old again.