How the Catholic Church elects a pope

Pope Benedict XVI announced on Monday he will resign as the head of the Roman Catholic Church on Feb. 28. 

A papal resignation is a rare event. The last time a pope resigned was nearly 600 years ago in 1415, when Pope Gregory XII stepped down to end infighting caused by two men competing for the papal chair.

Spokesman Federico Lombardi told reporters the Vatican expects a papal election by mid-March. But, how exactly does the Vatican elect its leader? 

It all begins with a meeting known as a "papal conclave," where the College of Cardinals elects a pope by ballot. The college, as you might expect, is a body of cardinals — usually over a hundred — that convenes at the Vatican to choose a successor after a pope's death or resignation.

A conclave starts no sooner than 15 days and no later than 20 days after a pope's death. In cases of resignation, the usual time of mourning does not have to be observed, according to the Associated Press. 

To vote, the cardinals enter the Sistine Chapel of the Apostolic Palace. They are prohibited from contact with the outside world, and all participants must take an oath, swearing absolute secrecy.

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If a candidate fails to receive a two-thirds majority vote, then four ballots — two in the morning, and two in the afternoon — are held each successive day until a two-thirds majority is reached. The conclave may elect any baptized male, though selecting a layman is highly unlikely. 

When the College of Cardinals fails to reach a two-thirds majority vote, the Vatican releases black smoke from a chimney on the Sistine Chapel, signaling an unsuccessful election. If a candidate wins enough votes, white smoke rises from the chimney, and the world's one billion faithful Catholics have their new leader.