The season of Easter is a joyous, celebratory season. It begins with celebrating Christ’s resurrection and ends by celebrating the descent of the Holy Spirit upon the Apostles and other followers of Jesus. Christ’s ascension into Heaven is celebrated just prior to Pentecost. The Easter season lasts through Pentecost.
While Easter marks the end of the paschal fast, the end of the celebration of Holy Week, and the end of repentance and conversion for which Lent prepared the community, it is much more a beginning. It is the beginning of a new season of grace and a time of joy and thanksgiving, for Easter is not one day or one solemnity—it is a fifty day celebration, and the fifty days from Easter Sunday to Pentecost Sunday together comprise what the General Instruction terms "the great Sunday".
In 2015, the Easter season starts with the Easter Vigil on Saturday, April 4, and ends on Pentecost Sunday on May 24.
Vigil and Easter Sunday
The celebration of the Easter Vigil is the beginning of the season of Easter. The Vigil and Easter Sunday are feasts of new birth, new beginnings, salvation renewed, and humanity restored to the Lord.
The Feast of Divine Mercy, celebrated on the Octave of Easter (the Sunday after Easter Sunday), is a relatively new addition to the Roman Catholic liturgical calendar. Celebrating the Divine Mercy of Jesus Christ, as revealed by Christ Himself to Saint Maria Faustina Kowalska, this feast was extended to the entire Catholic Church by Pope John Paul II on April 30, 2000, the day that he canonized Saint Faustina.
The Feast of the Ascension, 40th day of Easter, is a Holy Day of Obligation. The Feast commemorates Christ's Ascension into Heaven from Mount Olivet 40 days after He rose from the dead.
Pentecost Sunday, or Whitsunday, is the 50th day after Easter – counting both Easter and Pentecost. Pentecost commemorates the day (50 days after Jesus’ resurrection) when the apostles were gathered together and a flame rested upon the shoulders of the apostles and they began to speak in tongues (languages), by the power of the Holy Spirit.