The liturgical year begins with Evening Prayer I (traditionally called First Vespers) of the First Sunday of Advent. The season of Advent continues through the four Sundays of Advent and ends with the conclusion of Mid-afternoon Prayer on Christmas Eve.
Advent is a time of preparation, through fasting and prayer, for Christmas. Even though Christ was actually born over 2000 years ago, during Advent we prepare our hearts to “receive” Jesus into the world each year as a light to the nations, at a time when our calendar is reaching its darkest period. Advent is also a time of looking forward to Christ’s Second Coming in the last days.
At Christmas we celebrate the Word become flesh, coming to dwell among us as the light of the human race, just after the darkest point of the solar year. Christmas, therefore, is a holy day second only to Easter in the Roman calendar.
The Octave of Christmas (octave means eight; hence the octave of Christmas lasts for eight days) begins with Christmas day and ends after the Solemnity of Mary, Mother of God.
The season of Christmas ends, and Ordinary Time begins, on the Monday after the Solemnity of the Baptism of the Lord, which signifies the purification of the world, through Christ Himself.
Ordinary Time is not a season, like Advent, Christmas, Lent, and Easter. It is just a way of describing the weeks between seasons. We often think of “ordinary” as being something regular, plain, run of the mill. But it also has another meaning: “counted.” Ordinal numbers are first, second, third, fourth, etc. So, the Church is counting the weeks between the liturgical seasons.
There are two blocks of Ordinary Time. The first block is between the seasons of Christmas and Lent. The second block is between Easter and Advent. In total there are 34 weeks in Ordinary Time. On most days in Ordinary Time, the liturgical color is green. Each year at Sunday Mass for the majority of Ordinal Sundays, we read through one of the Gospels. This year, for the majority of Ordinal Sundays, we shall be following the Gospel according to St. Mark. (Cycle B).
The liturgical season of Lent lasts for 40 weekdays in remembrance of the 40 days and nights that Christ spent fasting in the desert, tempted by Satan. The beginning of Lent, Ash Wednesday, therefore comes 40 days (excluding Sundays) before Easter.
Lent, in commemoration of Christ’s fasting and prayer, is for all His faithful a time of fasting and prayer.
Because of the austerity of Lent, Alleluia is not said in prayer or sung in liturgy during this season.
The season of Easter begins at the Easter Vigil.
But before that, the week previous to Easter is called Holy Week; it begins with Passion Sunday (Palm Sunday) and culminates with the Triduum. The Triduum (a Latin word for a three-day period) begins with the Mass of the Lord’s Supper on the evening of the Thursday of Holy Week and includes Good Friday, and Holy Saturday.
Easter is such a special time—the celebration of our Lord’s resurrection, without which there would be no Christianity—that it continues not just for the joyful week following Easter (the Octave of Easter—each day celebrated as a solemnity of the Lord), but for 50 days (including Sundays and counting Easter Sunday itself) of the season of Easter.
The season of Easter comes to a close, and Ordinary Time returns, on the Monday after Pentecost Sunday.