Like Obama, Biden began his day early. He attended Catholic Mass at his official residence at the U.S. Naval Observatory a few miles from the White House. Justice Sonia Sotomayor, the first Hispanic justice and an Obama appointee, administered the oath of office.
Biden then joined Obama at the cemetery, where the two men placed a wreath at the Tomb of the Unknowns and observed a moment of silence as a bugler sounded "Taps."
Late Sunday, Biden made a surprise appearance at the Green Inaugural Ball, sponsored by the National Wildlife Federation and other environmental groups. "I don't intend to let these four years go by without getting a hell of a lot done" on the environment, he said.
Associated Press writers Darlene Superville, Josh Lederman, Matthew Daly and Stacy Anderson contributed to this report.
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