Papal conclave: Vatican holds last mass before papal election which could deliver result by 8pm TONIGHT Conclave to get under way in Sistine Chapel as church faces upheaval and uncertainty not seen in decades Catholics rudderless as there is no front-runner and no sense a single man has what it takes to fix problems Cardinals offer wildly different views over next pontiff and how close they were to a decision on eve of vote World's 1.2billion Catholics still in turmoil after Benedict XVI's shock resignation last month for health reasons 115 cardinals who are eligible to vote started the day with a mass in St Peter's Basilica at 10am local time They will enter Sistine Chapel at 4.30pm, intoning Gregorian chant imploring saints to help guide their voting They will then lock themselves inside until one candidate receives at least 77 votes required for victory Cardinals heard a final appeal for unity today before the conclave to elect the next pope as they celebrated Mass with the Catholic Church facing more upheaval and uncertainty than it has seen in decades. As a Gregorian chant filled St Peter's Basilica, the 115 cardinal electors filed in wearing bright red vestments, many looking grim as if the burden of the imminent vote was weighing on them. A few hundred people braved thunderstorms and pouring rain to watch the Mass on giant TV screens in St Peter's Square. A handful knelt in prayer, eyes clenched and hands clasped. In his homily, Cardinal Angelo Sodano, dean of the College of Cardinals, called for unity within the church, a not-so-veiled appeal to the cardinals to put their differences aside for the good of the church and the next pope. 'Each of us is therefore called to co-operate with the Successor of Peter, the visible foundation of such an ecclesial unity,' Sodano said. Pomp and circumstance: Cardinals attend a mass in St Peter's Basilica at the Vatican before entering the Sistine Chapel for conclave to elect the next pope He was interrupted by applause from the pews - not so much from the cardinals - when he referred to the 'beloved and venerated' Benedict XVI and his 'brilliant' pontificate. Benedict's surprise resignation - the first in 600 years by a pope - has thrown the church into turmoil and exposed the deep divisions among cardinals who are grappling with whether they need a manager who can clean up the Vatican's dysfunctional bureaucracy or a pastor who can inspire Catholics at a time of waning faith. 'Let us pray for the cardinals who are to elect the Roman pontiff,' read one of the prayers during the Mass. May the Lord fill them with his Holy Spirit with understanding and good counsel, wisdom and discernment. One of the faithful outside alluded to the huge challenge facing the next pontiff. 'It's a moment of crisis for the church so we have to show support of the new pope,' said Veronica Herrera, a real estate agent from Mexico who travelled to Rome for the conclave with her husband and daughter. This afternoon, 115 cardinals will file into the frescoed Sistine Chapel singing the Litany of Saints, a hypnotic Gregorian chant imploring the intercession of saints to help them choose a pope. They will hear a meditation by an elderly Maltese cardinal, take an oath of secrecy, and then cast their first ballots. The first puffs of smoke are expected to emerge from the chapel chimney by 8pm - black for no pope, white if a pope has been chosen. There is no front-runner in the election, no indication how long voting will last and no sense that a single man has what it takes to fix the church's many problems. Lonely figure: A pilgrim prays in St Peter's Square as cardinals attend mass before entering the conclave Day to remember: Nuns arrive to attend a mass at St Peter's Basilica on the first day of the conclave A good day to be inside: The Cardinals will lock themselves away in the Sistine Chapel until they have elected the new pope, who will need at least 77 votes to enter the papacy Dark clouds ahead: The cardinals have offered wildly different assessments of what they were looking for in the next pontiff and how close they were to a decision Stunning surroundings: Inside the Sistine Chapel, where conclave will start at 4.30pm local time today Ceremony: After another chant calling on the Holy Spirit to intervene, the cardinals take the oath of secrecy inside the Sistine Chapel, followed by a meditation delivered by elderly Maltese cardinal Prosper Grech