In a rare move, Pope Benedict XVI is retiring this week. (GIAMPIERO SPOSITO/REUTERS)

Pope Benedict XVI (that’s “16th” in Roman numerals) will make his last public speech on Wednesday, before retiring as the leader of the world’s 1.2 billion Roman Catholics on Thursday.

It was big news earlier this month when the pope announced he was going to retire. Given that he’s 85, you might think that’s just not a big deal. But no pope has resigned in almost 600 years. Usually, a pope serves until he dies.

The question of who will be the next pope will be answered when the church’s cardinals (a group of more than 100 senior church leaders) meet to vote. The meeting is called a conclave. Every time the cardinals vote, they burn the ballots. People watch the smoke rise out of the chimney of their meeting place. If it’s black, they haven’t agreed on a new pope. White smoke means a new pontiff (another word for pope) has been chosen.

The meeting will start soon, because the church wants to have a new pope in place before Easter on March 31.