"Because of God's presence in time in the person of Jesus Christ, time is sacred. Christians mark time itself in relation to Christ. The ... histroy of salvation unfolds throughout the liturgical year. Each day of the liturgical year is sanctified primarily by Christ's presence in it, but also by the prayer and liturgical celebrations of the People of God, especially by the Mass and the Divine Office. The liturgical year exerts 'a special sacramental power and influence which strengthens Christian life'."
-National Directory for Catechesis, p. 146
Liturgical Year
The calendar that guides the liturgies and prayers of the Church. It commences on the First Sunday of Advent and ends with the celebration of Christ the King. It includes Advent, the Christmas Season, Lent, the Easter Season, and Ordinary Time, as well as various Feasts of Mary, the Apostles, and many other saints.
The liturgical year is made up of six seasons:
The mystery of Christ, unfolded through the cycle of the year, calls us to live his mystery in our own lives. This call is best illustrated in the lives of Mary and the saints, celebrated by the Church throughout the year. There is no tension between the mystery of Christ and the celebration of the saints, but rather a marvelous harmony. The Blessed Virgin Mary is joined by an inseparable bond to the saving work of her Son, and the feasts of all the saints proclaim the wonderful works of Christ in his servants and offer the faithful fitting examples for their imitation.
Each liturgical year begins on the First Sunday of Advent during the preceding calendar year (i.e., the First Sunday of Advent in 2019 began the 2020 liturgical year).
Liturgical Calendar
The organization of each liturgical year is governed by the Church and ultimately integrated into a liturgical calendar.
The Second Vatican Council brought renewed emphasis to Sunday as a unique liturgical category: "the Lord's day is the original feast day" (Sacrosanctum Concilium, no. 106), and it "must be observed in the universal Church as the primordial holy day of obligation" (Code of Canon Law, canon 1246 §1). Thus, only a limited number of feasts of the Lord or the saints may take the place of the scheduled Sunday celebration.
Saints and other celebrations are distinguished in accordance with the importance assigned to each one: each is a Solemnity, Feast, or Memorial. Sundays and Solemnities begin their celebration on the evening before, Feasts and Memorials are celebrated over the course of one day, and Memorials are either Obligatory or Optional.
Holy days of obligation (also known as feasts of precept) are days when the faithful are obliged to participate at Mass and abstain from unnecessary work or other activities which hinder the suitable relaxation of mind and body. Each Sunday is a holy day of obligation, and six Solemnities are also observed as feasts of precept in the United States.
Finally, there are other days of prayer and special observances throughout the year that are promoted by the Holy See or the USCCB. For the most part, they are not part of the Church's liturgical calendar, but they can help focus the prayers of the Church toward the particular needs of the human family.
- taken from the USCCB Website