The Ascension of the Lord (colloquially known as Ascension Day) commemorates the bodily Ascension of Jesus into heaven. Ascension Day is traditionally celebrated on a Thursday, the fortieth day of Easter. The feast is one of the ecumenical feasts (i.e., universally celebrated), ranking with the feasts of the Passion, Easter, and Pentecost.
In Western Christianity, the earliest possible date is April 30th, the latest possible date is June 3rd.