VATICAN CITY -

Cardinals at the Vatican celebrated a final Mass Tuesday before sequestering themselves in the Sistine Chapel to begin the selection process for a new pope.

Cardinal Angelo Sodano, the dean of the College of Cardinals called from unity within the church when he delivered the homily at Saint Peter's Basilica. When he mentioned the name of the former pope Benedict, he was interrupted by applause from people in the pews.

Each of the 115 cardinals will cast a ballot to determine who will lead the world's 1.2 billion Catholic followers-- a task they say that is not being taken lightly.

"I think it is always something that is on the top of your mind," said Cardinal Theodore E. McCarrick, the retired Archbishop of Washington. "I am going to do now something, which will not just affect my life, but affect the lives all over the world."

After ballots are submitted, they are counted and burned. A smoke signal is then sent into the air, above the Sistine Chapel. White smoke means a new pope has been chosen, while black means the conclave will continue.

The process can be repeated up to four times a day, until someone gets 2/3 of the vote.