Rachel Donadio / New York Times News Service

VATICAN CITY — Benedict XVI ceased to be pope at 8 p.m. local time (11 a.m. Pacific) Thursday when his resignation took effect, leaving the leadership of the Roman Catholic Church vacant while its leading clerics consider who should succeed him.

Benedict left the Vatican by helicopter Thursday afternoon to spend the final hours of his scandal-dogged papacy and the first of his retirement at a summer residence used by popes for centuries. Onlookers in St. Peter’s Square cheered, church bells rang and Romans stood on rooftops to wave flags to see him off as he flew from Rome to the summer residence at Castel Gandolfo, a hilltop town southeast of the city.

Earlier in the day, in one of his concluding acts, Benedict addressed a gathering of more than 100 cardinals who will elect his successor, urging them to be “like an orchestra” that harmonizes for the good of the Roman Catholic Church. From a gilded throne in the Clementine Hall of the Apostolic Palace, the pope thanked the cardinals collectively, and then rose to greet each of them individually.

Draped in a red and gold mantle lined with snow-white ermine, Benedict clasped the hands of each cardinal as they removed their red skullcaps and kissed the pope’s ring. Benedict told them, “I will be close to you in prayer” as the next leader of the church is chosen.

Many of them were appointed to their powerful positions as so-called princes of the church by Benedict or by his predecessor, John Paul II, and are seen as doctrinal conservatives in their mold.

“Among you is also the future pope, whom I promise my unconditional reverence and obedience,” Benedict said.

As pope emeritus, Benedict intends to reside in Castel Gandolfo for several months and then return to the Vatican to live in an apartment being prepared for him in a convent whose gardens offer a perfect view of the dome of St. Peter’s Basilica.