VATICAN CITY (CNS) -- The cardinals who enter the Sistine Chapel May 7 to elect a new pope use smoke signals to communicate with the outside world.

Black smoke indicates they have cast their votes without anyone garnering the necessary two-thirds majority, while white smoke confirms that the Catholic Church has a new pope.

The best time to be in St. Peter's Square to see the smoke is just after 7 p.m. the first day of the conclave, May 7; and on the following days at 10:30 a.m. and noon, and again at 5:30 p.m. and just after 7 p.m.

Predicting when the smoke will rise from the chimney of the Sistine Chapel is not an exact science. The time needed for the cardinals' prayers, discussions and vote counting can vary.

The rules for a conclave are contained in the apostolic constitution, "Universi Dominici Gregis" ("Shepherd of the Lord's Whole Flock"), which was issued by St. John Paul II in 1996 and amended by Pope Benedict XVI in 2007 and again in 2013.

After the cardinals process into the Sistine Chapel to start the conclave and take their oaths of secrecy, the papal master of liturgical ceremonies proclaims "extra omnes" ("everyone out"), and the cardinals listen to 90-year-old Cardinal Raniero Cantalamessa, who they chose to offer a meditation "concerning the grave duty incumbent on them and thus on the need to act with right intention for the good of the Universal Church."

After that, there are prayers and an explanation of the rules for the election of a pope.

Then, the cardinals decide whether they want to cast their first ballots that same evening. The cardinals chose to have a first ballot in the evening during the 2005 conclave that elected Pope Benedict and the 2013 conclave that elected Pope Francis.

The cardinals' ballots, mixed with a chemical coloring, are burned in a stove in the Sistine Chapel.

In 2005 the black smoke from the first ballot was seen at 8:05 p.m. In 2013, black smoke from the first ballot was spotted at 7:41 p.m.

On the second day of the conclave and moving forward, there can be four rounds of voting each day, but only two smoke signals. That is because if the first ballot of the morning or of the afternoon session does not result in an election, a second vote begins immediately, and the two ballots are burned together.

During the conclave that elected Pope Francis, the set schedule called for the cardinals to celebrate Mass each morning at 8:15 a.m. in the Pauline Chapel of the Apostolic Palace and then go into the Sistine Chapel at 9:30 a.m. After a brief prayer, the first ballot of the day was to be cast, meaning that if a pope were elected the smoke would be seen at about 10:30 a.m. If no candidate received the required two-thirds of the votes, the cardinals would vote again and the two ballots would be burned at about noon, before the cardinals were to return to the Domus Sanctae Marthae for lunch and an afternoon break.

If this conclave follows the schedule set in 2013, the cardinals would return to the Sistine Chapel at 4 p.m. and continue voting. If someone were to be elected on the first afternoon ballot, the smoke would be visible at about 5:30 p.m. If no one were elected, the smoke from evening ballots would come shortly before the cardinals were to return to the Domus Sanctae Marthae at about 7:30 p.m. for dinner and to sleep.