WASHINGTON - President Barack Obama took the oath of office Sunday surrounded by family in an intimate inauguration ceremony at the White House.

The subdued swearing-in was a function of the calendar and the Constitution, which says presidents automatically begin their new terms at noon on Jan. 20. Because that date fell this year on a Sunday - a day on which inaugural ceremonies historically are not held - organizers scheduled a second, public swearing-in for Monday.

A crowd of an estimated 800,000 people gathered on the National Mall to witness the second inauguration.

Vice President Joe Biden was also be sworn in Sunday in a small, early morning ceremony at the Naval Observatory, his official residence.

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