Catholics observe Easter in different stages. Easter Sunday is the greatest Sunday of the year, and it marks the start of the “Easter Octave,” or the eight days that stretch from the first to the second Sunday of Easter (also known as Divine Mercy Sunday). The Church celebrates each of these eight days as Solemnities of the Lord — a direct extension of Easter Sunday.
The entire Easter season lasts 50 days, and includes the Solemnity of the Ascension of Christ, which falls on the 40th day of Easter, which this year is May 26. It ends with Pentecost, which is derived from the Greek word "pentecoste," meaning “50th.”
“The fifty days from the Sunday of the Resurrection to Pentecost Sunday are celebrated in joy and exultation as one feast day, indeed as one ‘great Sunday,’” according to the United States Conference of Catholic Bishops. “These are the days above all others in which the Alleluia is sung.”
The USCCB calls Easter “the most important of all liturgical times.”
“It celebrates Jesus's victory of sin and death and salvation for mankind,” the U.S. bishops say. “It is God's greatest act of love to redeem mankind.”
In the traditional Roman rite