Though each calendar year there are seasons in which the church enters. Just like summer, winter and fall, the church also has seasons. Most people are familiar with the names of each of the liturgical calendar. The season are Advent, Christmas, Lent, Easter and of course, Ordinary Time. These are the basic division of how the Liturgical Calendar is divided.
The churches use this way to decide what readings are used, when Feast Days and Solemnities are observed. Many of the Solemnities are placed though the calendar based on dates. In both Easter and western sects of Christianity the dates of the feast days may be vary from year to year. Things like Easter are the prime example. Easter's date is set within the Catholic Church by picking the first Sunday after the first full moon after the spring equinox. That sets the date for Easter, which you then count back 6 weeks and there you have the start of Lent.
The date that Easter falls on also dictates a number of Solemnities, a day the Catholic Church has set aside and most correspond with an event in Christ.s life. The other Solemnities in the Catholic Church that are determined by the day within the liturgical calendar are The Ascension of the Lord, which is always 40 days after Easter, but moved to the following Sunday in some parts of the US. Pentecost is the 50th day after Easter. The Holy Trinity is always the Sunday after Pentecost.
There are also dates that are based off the date of Christmas although there are some Solemnities though the Liturgical Calendar that are a set and prescribed dates. For example. Dec 8 is always the Immaculate Conception, but the feast of Christ the King, is always the last Sunday before Advent. How advent is determined is to take Christmas go to the Sunday before it and count four Sundays prior to Christmas Day. Usually the Feast of Christ the King will fall during Thanksgiving weekend but not always.
Additionally, the other thing the Catholic Church does is they have divided up the readings in to 3 year cycles which over the course of those three years. If you read each daily reading you will have read the entire Bible. Most Catholics don.t know that to be the case and only think of what they hear each Sunday only. But each Sunday of time has a week attached to it though each of these seasons.
Additionally the Liturgical seasons have distinctive colors, Green, Purple, Red, Pink, White. If you walk into any Catholic church you would know what season it is based on vestment color. The Green vestment is the most prevalent and applies to ordinary time. The Pink Vestment is For the third week of Advent. The Purple Vestments are worn during penitential or atonement seasons of Advent and Lent. White Vestments are for the Liturgical Calendar periods of Christmas and Easter Seasons. And lastly there is Red vestments which are not indicative of a period of time but the blood of the martyrs. On a Feast day of a Martyr, the priest will wear red vestments during mass as well as the cardinals who are bishops who have vowed to die for Christ if the situation arises.
