Celebrated opera singer Plácido Domingo was all smiles during an appearance at Harvard this week. The legendary tenor was at Sanders Theatre, where he talked about some of his memorable performances, his directorship of the Los Angeles Opera and career as a conductor, and his advocacy for Hispanic and Latino arts and culture. The 75-year-old Spaniard had been scheduled to speak last fall, but postponed to have gallbladder surgery. As a tiny token of appreciation, Diana Sorensen, dean of Arts and Humanities at Harvard, presented Domingo with a letter jacket, and he seemed genuinely pleased to receive it. . . . Meanwhile, US diplomat Dennis Ross, a Middle East expert who served presidents George H.W. Bush and Bill Clinton, said something we didn’t know during an appearance at Symphony Hall as part of Lesley University’s speakers series. According to Ross, late Palestine Liberation Organization leader Yasser Arafat was fascinated with “The Golden Girls,’’ the NBC sitcom starring Bea Arthur, Betty White, Rue McClanahan, and Estelle Getty.