Pentecost always occurs 50 days after the resurrection of Jesus and 10 days after his ascension into heaven. Because Easter is a moveable feast without a fixed date, and Pentecost depends on the timing of Easter, Pentecost can fall anywhere between May 10 and June 13.

The timing of these feasts is also where we get the concept of the novena — nine days of prayer — because in Acts 1, Mary and the Apostles prayed together “continuously” for nine days after the Ascension leading up to Pentecost. Traditionally, the Church prays the novena to the Holy Spirit in the days before Pentecost.

The name of the day itself is derived from the Greek word “pentecoste,” meaning 50th.

In the Christian tradition, Pentecost is the celebration of the person of the Holy Spirit coming upon the Apostles, Mary, and the first followers of Jesus, who were gathered together in the Upper Room.

A “strong, driving” wind filled the room where they were gathered, and tongues of fire came to rest on their heads, allowing them to speak in different languages so that they could understand each other. It was such a strange phenomenon that some people thought the Christians were just drunk — but Peter pointed out that it was only the morning, and said the phenomenon was caused by the Holy Spirit.

The Holy Spirit also gave the apostles the other gifts and fruits necessary to fulfill the great commission — to go out and preach the Gospel to all nations. It fulfills the New Testament promise from Christ (Luke 24:46-49) that the Apostles would be “clothed with power” before they would be sent out to spread the Gospel.

Pentecost is considered the birthday of the Church — Peter, the first Pope, preaches for the first time and converts thousands of new believers. The apostles and believers, for the first time, were united by a common language, and a common zeal and purpose to go and preach the Gospel.

Typically, priests will wear red vestments on Pentecost, symbolic of the burning fire of God’s love and the tongues of fire that descended on the apostles.