Q: When are Cyril and Methodius celebrated?
Cyril and Methodius's national as well as Roman Catholic holiday in Slovakia is on 5 July, but the Vatican's currently applicable world-wide General Roman Calendar makes it a memorial (a lower-ranked, 3rd-class holiday) on 14 February. The small Greek Catholic Church in Slovakia and the tiny Orthodox Church celebrate Sts. Cyril and Methodius's holiday on 24 May (marked as 11 May in their Julian calendar), but also join the national celebrations on 5 July.
1584 Martyrology, 9 March
The Vatican's Martyrology that came out of the guiding Council of Trent recorded their feast on 9 March. Its first English translation read:
March. [...] The nynth Day [...] In Moravia of the holy Saints Cyrillus and Methodius Biſhops, who couerted to the fayth of Chriſt many Countreyes, together with their Kinges, in thoſe parts.
1863 Millennium, 5 July
Before the millennial celebrations of the arrival of Cyril and Methodius in Great Moravia, Friedrich Fürstenberg, Archbishop of Olomouc, Moravia, requested a transfer of the holiday from 9 March to 5 July (which was a Sunday in 1863).
His appeal to Pope Pius IX argued that people could not travel to the planned massive festivities as easily, and therefore not in large numbers, on 9 March during the cold and muddy season and that Lent was not an appropriate time for a joyful festival.
Rome's prompt permission indicates that the requested date, 5 July, had already been consulted with the Vatican (there is no recognized July event in Cyril's or Methodius's lives) and chosen also in an effort to counterbalance the increasingly frequent commemorations of the dissident priest Jan Hus on 6 July. The Vatican had him burned at the stake on that date in 1415, and Czech ethnic activists began to promote him in the 19th century as a symbol of their anti-Habsburg dissent.
1864+ Moravia, 5 July
Pope Pius IX allowed the Margraviate of Moravia, and the Kingdoms of Bohemia and Croatia to keep the new date, which eventually applied to the Slovaks too, e.g., the Banská Bystrica diocese in 1865, the Košice archdiocese in 1883.
1880 Roman Catholics, 5-7 July
Pope Leo XIII then extended 5 July to the whole Roman Catholic Church in his encyclical of 30 September 1880. The official Roman Catholic day was shifted to 7 July seven years later to avoid crowding out a saint popular elsewhere, but the celebrations largely remained on the 5th in Slovak, Moravian, and Czech parishes.
Pope Leo XIII's encyclical also took the opportunity to state that Cyril and Methodius, who had not been formally cannonized by the Vatican (Pius IX did not call them saints when he granted the date shift), carried out deeds that made them holy men and called them Saints Cyril and Methodius. The Vatican did not launch formal cannonizations until the late 10th century. Personalities from earlier periods have been accepted as saints through tradition. For instance, the Vatican's 16th-century Martyrology called Cyril and Methodius saints.
1969, 14 February
The new authoritative Calendarium Romanum adopted under Pope Paul VI shifted the Church-wide commemoration of Sts. Cyril and Methodius to 14 February, the accepted date of Cyril's death. The Vatican generally associates feast days with events in the saints' lives, while there is no known July event in Cyril's or Methodius's lives. 14 February has been retained through the present.
Slovakia, 5 July
The dioceses of Slovakia and the Czech-speaking territories, though, were able to continue their by-then traditional celebrations on 5 July.
The Parliament legislated 5 July as a national holiday, "Sts. Cyril and Methodius Holiday," in Slovakia on 9 May 1990.
The Greek Catholic Church in Slovakia celebrates Cyril and Methodius's supposed arrival in Great Moravia on 24 May (marked as 11 May in its Julian calendar) and also joins the national celebrations on 5 July.