WASHINGTON (AP) – Vice President Joe Biden has been sworn in to a second term.

The 70-year-old Biden took the oath of office from Supreme Court Justice Sonia Sotamayor during a private ceremony Sunday at the U.S. Naval Observatory, the vice president’s residence.

President Barack Obama takes the official oath of office around midday in an intimate ceremony at the White House.

The subdued swearing-in is 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 up to 800,000 people is expected to gather on the National Mall to witness the second inauguration tomorrow at the Capitol.