When Did the Holy Spirit Come Down on the Apostles?

After Christ's Ascension, the Apostles were uncertain what would happen. Along with the Blessed Virgin Mary, they spent the next ten days in prayer, waiting for a sign. They received it in tongues of fire when the Holy Spirit descended upon them.

What Does the Baltimore Catechism Say?

Question 97 of the Baltimore Catechism, found in Lesson Eighth of the First Communion Edition and Lesson Ninth of the Confirmation Edition, frames the question and answer this way:

Question: On what day did the Holy Ghost come down upon the Apostles?

Answer: The Holy Ghost came down upon the Apostles ten days after the Ascension of our Lord; and the day on which He came down upon the Apostles is called Whitsunday, or Pentecost.

With its roots in the 19th century, the Baltimore Catechism uses the term Holy Ghost to refer to the Holy Spirit. While both the Holy Spirit and Holy Ghost have a long history, Holy Ghost was the more common term in English until the late 20th century.

The Roots of Pentecost

Because Pentecost is the day on which the Apostles and the Blessed Virgin Mary received the gifts of the Holy Spirit, we tend to think of it as an exclusively Christian feast. But like many Christian feasts, including Easter, Pentecost has its roots in Jewish religious tradition. The Jewish Pentecost fell on the 50th day after Passover, and it celebrated the giving of the law to Moses on Mount Sinai. It was also, as Fr. John Hardon notes in his Modern Catholic Dictionary, the day on which "the first fruits of the corn harvest were offered to the Lord" in accordance with Deuteronomy 16:9.

Just as Easter is the Christian Passover, celebrating the release of mankind from the bondage of sin through the death and Resurrection of Jesus Christ, the Christian Pentecost celebrates the fulfillment of the Mosaic law in a Christian life led through the grace of the Holy Spirit.

Jesus Sends His Holy Spirit

Before He returned to His Father in Heaven at the Ascension, Jesus told His disciples that He would send His Holy Spirit as their comforter and guide, and He ordered them not to leave Jerusalem. After Christ ascended into Heaven, the disciples returned to the upper room and spent ten days in prayer.

On the tenth day:

"suddenly there came from the sky a noise like a strong driving wind, and it filled the entire house in which they were. Then there appeared to them tongues as of fire, which parted and came to rest on each one of them. And they were all filled with the Holy Spirit and began to speak in different tongues, as the Spirit enabled them to proclaim".

Filled with the Holy Spirit, they began to preach the Gospel of Christ to Jews "from every nation under heaven" who were gathered in Jerusalem for the Jewish feast of Pentecost.

Why Whitsunday?

The Baltimore Catechism refers to Pentecost as Whitsunday (literally, White Sunday), the traditional name of the feast in English, though the term Pentecost is most commonly used today. Whitsunday refers to the white robes of those who were baptized at the Easter Vigil, who would don the clothes once again for their first Pentecost as Christians.