The Solemnity of the Ascension of Our Lord.
A Holy Day of Obligation, meaning that Catholics around the world are obliged to participate in Holy Mass. In parts of the United States and other countries in which Catholic Holy Days are not public holidays, the day of Obligation is commuted to the 7th Sunday of Easter.
Ascension Thursday observes the Ascension of Christ into Heaven witnessed by the apostles 40 days after His resurrection from the dead.
The feast was celebrated by the apostles themselves, the original bishops of the Catholic Church, lending credibility to the the date of the Resurrection, which is Traditionally preserved as having taken place on March 25th. The true date of Easter is determined yearly by astronomical means in order to ensure it's accuracy, making Easter, Ascension and Pentecost "movable" feasts, occurring on different calendar dates every year. Christ's Ascension is always observed on the 6th Thursday of Easter, 40 days after the Resurrection.
