Editing Leap year (section)

===Liturgical practices===
[[File:MissaleLeapYear.jpg|thumb|right|In the older [[Roman Missal]], feast days falling on or after 24 February are celebrated one day later in a leap year.]]
In the [[liturgical calendar]] of the Christian churches, the placement of the leap day is significant because of the date of the feast of [[Saint Matthias]], which is defined as the sixth day before 1 March (counting inclusively). The Church of England's ''[[Book of Common Prayer]]'' was still using the "two days with the same date" system in its 1542 edition;<ref>{{Citation |last1=Campion |first1=Rev W M |url=https://archive.org/details/prayerbookinter01unkngoog/page/n50/mode/2up |title=The Prayer Book interleaved |last2=Beamont |first2=Rev W J |date=1870 |location=London |publisher=Rivingtons |page=31 |via=[[Archive.org]]}}</ref> it first included a calendar which used entirely consecutive day counting from 1662 and showed leap day as falling on 29 February.<ref name="Baskerville">{{Citation |last=Church of England |url=https://archive.org/details/bookcommonpraye00chur/page/n25/mode/1up |title=Book of Common Prayer |publisher=[[John Baskerville]] |year=1762 |location=Cambridge |orig-year=1662 |via=[[Archive.org]]}}</ref> In the 1680s, the Church of England declared 25 February to be the feast of St Matthias.{{sfnp|Cheney|2000|p=8}}
Until 1970, the [[Roman Catholic Church]] always celebrated the feast of Saint Matthias on {{lang|la|a. d. VI Kal. Mart.}}, so if the days were numbered from the beginning of the month, it was named 24 February in common years, but the presence of the {{lang|la|bissextum}} in a bissextile year immediately before {{lang|la|a. d. VI Kal. Mart.}} shifted the latter day to 25 February in leap years, with the [[Vigil]] of St. Matthias shifting from 23 February to the leap day of 24 February. This shift did not take place in pre-Reformation Norway and Iceland; [[Pope Alexander III]] ruled that either practice was lawful.<ref>[[Liber Extra]], 5. 40. 14. 1</ref> Other feasts normally falling on 25–28 February in common years are also shifted to the following day in a leap year (although they would be on the same day according to the Roman notation). The practice is still observed by those who use the older calendars.{{citation needed|date=February 2024}}

In the [[Eastern Orthodox Church]], the feast of St. [[John Cassian]] is celebrated on 29 February, but he is instead commemorated at Compline on 28 February in non-leap years. The feast of St. Matthias is celebrated in August, so leap years do not affect his commemoration, and, while the feast of the [[Beheading of John the Baptist#Related feasts|First and Second Findings of the Head of John the Baptist]] is celebrated on 24 February, the Orthodox church calculates days from the beginning of the current month, rather than counting down days to the Kalends of the following month, this is not affected. Thus, only the feast of St. John Cassian and any movable feasts associated with the Lenten or Pre-Lenten cycles are affected.