The Feast of the Ascension is one of the great feasts in the Christian liturgical calendar, and commemorates the bodily Ascension of Jesus into heaven. Ascension Day is traditionally celebrated on a Thursday, the fortieth day from Easter day.
However, some Roman Catholic provinces have moved the observance to the following Sunday. The feast is one of the ecumenical feasts (i.e., universally celebrated), ranking with the feasts of the Passion, of Easter and Pentecost.
The observance of this feast is of great antiquity. Although no documentary evidence of it exists prior to the beginning of the 5th century, St. Augustine says that it is of Apostolic origin, and he speaks of it in a way that shows it was the universal observance of the Church long before his time. Frequent mention of it is made in the writings of St. John Chrysostom, St. Gregory of Nyssa, and in the Constitution of the Apostles. The Pilgrimage of Aetheria speaks of the vigil of this feast and of the feast itself, as they were kept in the church built over the grotto in Bethlehem in which Christ was born.
It may be that prior to the 5th century the fact narrated in the Gospels was commemorated in conjunction with the feast of Easter or Pentecost. Some believe that the much-disputed forty-third decree of the Council of Elvira (c. 300) condemning the practice of observing a feast on the fortieth day after Easter and neglecting to keep Pentecost on the fiftieth day, implies that the proper usage of the time was to commemorate the Ascension along with Pentecost. Representations of the mystery are found in diptychs and frescoes dating as early as the 5th century.