(AP) _ President Barack Obama promised to uphold the Constitution in a public swearing in ceremony that signals the beginning of his second term in office.

Placing his hand on two Bibles -- one used by President Abraham Lincoln at his first Inauguration and one used by the Reverend Dr. Martin Luther King, Jr. -- Obama took a public oath of office on Monday, after he was sworn in during a private ceremony on Sunday. The Constitution requires presidential terms to begin on Jan. 20.

Supreme Court Chief Justice John Roberts administered Obama's private swearing in on Sunday and the public ceremony Monday. He also swore Obama in during his first inauguration in 2009.

After a bitterly partisan election and lame-duck session, Barack Obama is using his speech to call for a divided nation to come together to right the nation's course.

``Now more than ever we should do this as one nation,'' Obama says, adding that Americans are made for this moment and can succeed ``so long as we seize it together.''

``We remember the lessons of our past ... we do not believe in this country that freedom is reserved for the lucky or happiness for the few,'' Barack Obama said. ``We the people still believe that our obligations as Americans are not just to ourselves but to all posterity.''

President Barack Obama emphasized three prongs of civil rights, declaring, ``We, the people, declare today that the most evident of truths _ that all of us are created equal _ is the star that guides us still.''

He went further, with direct mentions of equality regardless of race, gender and sexual orientation. He referenced both Selma and Stonewall _ landmark events for black and gay Americans, respectively _ and talked of our country finally seeing its wives and mothers earning an ``equal living'' for the work that they do.

``It is our generation's task to carry on what those pioneers began,'' he said on this day, which is also Martin Luther King Day in the United States.

From the same podium where President Obama stood today, Ronald Reagan famously said that in the present crisis government is not the solution, government is the problem. Three decades on, emerging from another, even deeper crisis, Obama said government is, at least part of the solution.

Americans remain skeptical of central authority and have never succumbed to the fiction that government is the total solution, he said.

``But we have always understood that when times change, so must we; that fidelity to our founding principles requires new responses to new challenges; that preserving our individual freedoms ultimately requires collective action,'' Obama said.