The next upcoming Ascension Day is on Thursday May 21st, 2020.
This day known as Ascension Thursday or Holy Thursday or more popular referred to as Ascension Day commemorates the ascension of Jesus into heaven on the fortieth day of Easter celebrated by a feast. The end of easter season is marked by Ascension Day and its ten days before Pentecost. In the Catholic church the day if referred to as The Ascension of the Lord. This day is not a national holiday but rather an observance nationally recognized by Christians.
Prior to the 5th century very little information exists about the observance of the feast but St Augustine says it is of Apostolic orgin and that it was a common observance in the church. Various other Saints have writings referring to the feast including St John Chrysostom and St Gregory of Nyssa.