Pentecost or Whit Sunday(Whitsun)

"Pentecost" is from Greek meaning "fiftieth." The name Pentecost was originally given to the Jewish Feast of Weeks(Shavuot) which fell on the fiftieth day after Passover. Originally this feast lasted for seven days. On Shavuot the Jews celebrates that the Torah was given to them on the Mount Sinai, and the wheat is riped for harvest.

Pentecost by Duccio di Buoninsegna. Museo dell'Opera del Duomo, Siena, Italy

Pentecost begins 50 days after Easter Sunday. This liturgical season celebrates the descent of the Holy Spirit upon the Church and apostles. ( Acts 2:1-41)

The Vigil of Pentecost, like the Vigil of Easter, used to be a day for baptism. It had an almost similar liturgy as the Easter Vigil. The newly batised were clothed i white garments and therof comes the name Whitsunday.

Like the Church celebrates the Octave for Christmas and Easter, it also used to celebrate the Pentecost Octave in similar manner. In Norway we have a remainder of this on the Second Day of Pentecost (Whitmonday)