THE LITURGICAL YEAR
The Liturgical Year is an annual cycle of seasons and feasts that celebrates the Paschal Mystery, especially focusing on Christ's Death and Resurrection (Easter Cycle), and Birth (Christmas Cycle). The Catechism of the Catholic Church states that "In the Liturgical Year the various aspects of the one Paschal mystery unfold. This is also the case with the cycle of feasts surrounding the mystery of the incarnation (Annunciation, Christmas, Epiphany). They commemorate the beginning of our salvation and communicate to us the first fruits of the Paschal mystery." (CCC 1171)
The celebration of the Liturgical Year is meant to draw the Catholic faithful into the Mystery of Christ, helping them to experience His divine life more fully and deeply. This includes remembering and celebrating the lives of the saints, especially Mary, the Mother of God: "By keeping the memorials of the saints - first of all the holy Mother of God, then the apostles, the martyrs, and other saints - on fixed days of the Liturgical Year, the Church on earth shows that she is united with the liturgy of heaven. She gives glory to Christ for having accomplished his salvation in his glorified members; their example encourages her on her way to the Father." (CCC 1195)
The Western and Eastern rites of the Catholic Church hold the major feast days and seasons in common, but differ on many of the solemnities and feasts. Below are the most important feast days, plus some of the feasts unique to the Eastern Catholic Churches. We have divided them into two categories those that a stationary and are always celebrated on the same day of the calendar year and those that move because they belong to the paschal cycle and such move according to when Easter is celebrated.
Taken from http://nativityukr.org/parish_life/liturgical_calendar.html