Tomorrow night many of the world’s 300 million Orthodox believers will gather in their churches to see in Easter. The great feast will arrive with a blaze of candlelight and a blast of choral singing. On the following day, Catholics will mark the Sixth Sunday of Easter. In places where large numbers of Orthodox and Catholic believers live side by side, the effect is bizarre: to outsiders, there seem to be two Easters a month apart. As Pope Francis has joked, Catholics and Orthodox could say to one another: “When did Christ rise from the dead? My Christ rose today, and yours next week.” The reason for the different Easter dates is simple: the Eastern Orthodox use the Julian Calendar, established in 46 BC, while Catholics follow the Gregorian Calendar, introduced in the 16th century. Sometimes Orthodox and Catholic Easters fall on the same day (as they will in 2017). In other years, such as this one, they are as many as five weeks apart. The disagreement over the date of Easter suggests the vast psychological distance between the two communions. Many Catholics know little about the Orthodox, and vice versa. Where there isn’t ignorance, there is sometimes mistrust: the bitter fruit of almost 1,000 years of separation. But this year could potentially be a happy one for Catholic-Orthodox relations. In June Orthodox leaders will gather in Crete for the Holy and Great Synod of the Orthodox Church. Dubbed “the Orthodox Vatican II” (though the analogy is imperfect), this gathering has been in preparation since 1961. One of the six items on the agenda is “Relations of the Orthodox Church with the Rest of the Christian World”. Pope Francis has made two big moves this year that seem designed to nudge the synod in a pro-Rome direction. The first was his historic meeting with Russian Orthodox leader Patriarch Kirill in Havana this February. The encounter disturbed Ukrainian Catholics, but marked a breakthrough in relations with one of the most influential of the 14 self-governing Orthodox churches. The second was the Pope’s visit to Lesbos, flanked by the Ecumenical Patriarch of Constantinople and the Orthodox Archbishop of Athens. The trip was a beautiful illustration of the Pope’s conviction that Catholics and other Christians should draw closer through shared acts of charity. Francis’s hope must be that when the Orthodox hierarchy discuss ecumenism in June they will realise that the Catholic Church is committed to seeking unity in word and deed. In 2007, Catholic and Orthodox theologians reaffirmed that the Bishop of Rome is the protos, or first, among bishops. Francis has gone to great lengths to show that this position is not one of dominance but service. We will find out soon if he has persuaded Orthodox leaders that the Pope is not an enemy but an ally.