good morning. i'm brianna keilar in for brandy kay. thanks for starting your morning with us. first up, the cardinals who will choose the next spiritual leader of the roman catholic church are spreading out to celebrate masses. tuesday, they will all be in one place. the vatican. cnn's jonathan mann walks us through the top secret process to pick the new pope. >> it's the oldest enduring electoral system in the world. many of its traditions have been unchanged for centuries. the conclave, which literally means locked with a key, dates back to a time when cardinals were locked in until they chose a new pope. now, it's the world that's locked out figuratively speaking, as much of the conclave will take place behind closed doors. the gathering begins with a morning mass in st. peter's basilica. in the afternoon, the 115 voting cardinals, those under 80 years old, en certificate the sistine chapel where they will each take on oath of secrecy.