The Orthodox church calendar is the schedule by which the Church lives, divine services are held, and fasts begin. The Church has twelve major holidays, which are called: the Twelve. And the Trinity festival is one of them. Easter is considered the main Orthodox holiday; it is not even among the twelve. Easter is a “holiday celebration” - an event that defines church life for a good third of the year. Moreover, the date of several twelfth holidays, including the Trinity, can be determined precisely by Easter.
Easter is a passing holiday, that is, every year it happens at different times. The date of Easter is difficult to calculate, and the time of the onset of a number of important events depends on it.
Before Easter, Christians around the world have a fast. Among the Orthodox, this is Lent, which begins seven weeks before the Holy Christ Resurrection. Before Lent, there are several special weeks for preparation: a week about Zacchaeus, a week with reading about the Publican and the Pharisee, a week dedicated to the prodigal son, a week about the Last Judgment (aka Shrovetide).
That is, preparation for Easter begins in 13 weeks. After Easter there is a series of holidays that are associated with it. This is Fomin’s week, and the week of the Myrrh-Bearing Women, Ascension, Trinity. What number of Trinity in a particular year depends on what number Easter falls on.
The Trinity happens on the fiftieth day after Easter, therefore it is also called Pentecost.
What is the number of the Trinity, it’s easy to calculate, knowing the date of Easter or the beginning of Great Lent. 50 days should be added to the Easter Date, and 14 weeks to the day of Great Lent. Orthodox publishers often print small Easter calendars, which indicate what day Easter will be, and what date the Trinity will be, a decade ahead.
One week after the feast of Pentecost, the fast of Peter begins . It always ends on July 12, the day of the holy apostles of the supreme saints Peter and Paul.
Easter and, therefore, the Trinity is early and late, and the beginning of the Peter Lent can also be early and late. Since this post always ends on July 12, its duration depends on what date the Trinity holiday is. Petrovka, that is, the
Petrovsky post, is not strict, but its duration is different each time: from two weeks to six.
Any post imposes significant restrictions on all who comply with it. Lent implies not only the rejection of fast food, but also the restriction of entertainment, frequent attendance of worship. Some do not watch TV in fasting, do not go to the theater or to visit. Life in fasting is changing dramatically, so the Orthodox will be very interested to know the date of Easter for next year or what date of the Trinity. For example, Trinity 2013, what date? It is necessary to open Easter and find out that Easter in 2013 is very late, and Trinity falls on June 23. This means that Lent this year will begin late, and indeed, the beginning of the Lent fell on March 15. Everyone calmly and without worries celebrated March 8, and Easter fell on May holidays, which is also very convenient. Petrov's post was short, only two weeks.
Some are surprised that the Orthodox use such an indefinite, each time different calendar. But besides theological justifications, there are other positive aspects of such an “instability”. Each year is different, one is not like the other, and this is not bad.