The fifty days from Easter Sunday to Pentecost are celebrated in joyful exultation as one feast day, or better as one 'great Sunday'. These above all others are the days for the singing of the Alleluia.
The Sundays of this season rank as the Sundays of Easter and, after Easter Sunday itself, are called the Second, Third, Fourth, Fifth, Sixth, and Seventh Sundays of Easter. The period of fifty sacred days ends on Pentecost Sunday.
The first eight days of the season of Easter make up the octave of Easter and are celebrated as solemnities of the Lord.
On the fortieth day after Easter the Ascension of the Lord is celebrated, except in places where, not being a holy day of obligation, it has been transferred to the Seventh Sunday of Easter.
The weekdays after the Ascension of the Lord until the Saturday before Pentecost inclusive are a preparation for the coming of the Holy Spirit, the Paraclete
Sacred Congregation of Divine Worship, General Norms for the Liturgical Year and the Calendar, n22-26
The Easter season begins on the evening of Easter Sunday and continues for fifty days, ending on the evening of Pentecost Sunday. The eight days following Easter are observed as the Octave of Easter and each day has the same solemnity as a Sunday. If another solemnity falls during the octave it is transferred to the following Monday.
The fifty days between Easter and Pentecost are a time of joy and thanksgiving for what Christ has done for humanity. The paschal candle is in a prominent place in the sanctuary of the church and is lit for all liturgical celebrations.
In New Zealand the Ascension is celebrated on the Seventh Sunday after Easter. The feast of the Ascension commemorates the ascension of Jesus into heaven after his resurrection.
One week after the Ascension, on the 50th day after Easter, the feast of Pentecost is celebrated. Pentecost commemorates the outpouring of the Holy Spirit on the apostles, which empowered them to go out and begin spreading the Gospel. On Pentecost Sunday we celebrate the founding of the Church (sometimes called “the birthday of the Church”) and the beginning of its mission to all peoples.
The liturgical colour of most of the Easter season is white. The liturgical colour for Pentecost is red, which symbolises the Holy Spirit and the tongues of fire which appeared above the heads of the apostles when they received the Holy Spirit.