Moveable Feasts
The moveable feasts are those connected with the Easter cycle, and Easter is the date relative to which their position is ultimately determined. The date of Easter is determined relative to the lunar calendar as used by the Hebrews. The rule has since the Middle Ages been phrased as “Easter is observed on the Sunday after the first full moon on or after the day of the vernal equinox.” However, this does not reflect the actual ecclesiastical rules precisely. One reason for this is that the full moon involved (called the Paschal full moon) is not an astronomical full moon, but an ecclesiastical moon. Another difference is that the astronomical vernal equinox is a natural astronomical phenomenon, which can fall on 20 or 21 March, while the ecclesiastical vernal equinox is a fixed March 21 (on the Gregorian Calendar). Easter is determined from tables which determine Easter based on the ecclesiastical rules described above, which do not always coincide with the astronomical full moon. The moveable feasts are given below:
Septuagesima Sunday (9th Sunday before Easter)
Sexagesima Sunday (8th Sunday before Easter)
Quinquagesima Sunday (7th Sunday before Easter)
Ash Wednesday (Wednesday after Quinquagesima Sunday)
Passion Sunday (Sunday 2 weeks before Easter)
Feast of the Seven Sorrows of the Virgin Mary (Friday after 2nd Sunday before Easter)
Palm Sunday (Sunday before Easter)
Holy Thursday (Thursday before Easter)
Good Friday (Friday before Easter)
Holy Saturday (Saturday before Easter)
Easter Sunday, the Solemnity of Solemnities, the Resurrection of Our Lord Jesus Christ
Low Sunday (Sunday after Easter)
The Solemnity of St. Joseph, spouse of the Virgin Mary, confessor, and patron of the Universal Church (Wednesday after the 2nd Sunday after Easter)
The Octave of St. Joseph, spouse of the Virgin Mary, confessor and patron of the Universal Church (Wednesday after the 3rd Sunday after Easter)
The Lesser Litanies at St. Mary Major (Monday after the 5th Sunday after Easter)
The Lesser Litanies at St. John Lateran (Tuesday after the 5th Sunday after Easter)
The Vigil of the Ascension of our Lord Jesus Christ and the Lesser Litanies at St. Peter's (Wednesday after the 5th Sunday after Easter)
The Ascension (Thursday after the 5th Sunday after Easter)
The Octave of the Ascension (Thursday after the 6th Sunday after Easter)
The Vigil of Pentecost (Saturday after the 6th Sunday after Easter)
Pentecost (7th Sunday after Easter)
Holy Trinity and the Octave of Pentecost (8th Sunday after Easter)
Corpus Christi (Thursday after the 8th Sunday after Easter)
Octave of Corpus Christi (Thursday after the 9th Sunday after Easter)
Sacred Heart of Jesus (Friday after the 9th Sunday after Easter)
Octave of the Sacred Heart of Jesus (Friday after the 10th Sunday after Easter)
The 1954 calendar assigned special celebrations also to the days within these Octaves, as to the days within the Octaves of fixed feasts.
Read more about this topic: General Roman Calendar Of 1954