Ascension Day occurs ten days before Pentecost and it always falls on a Thursday. However, some churches, particularly in the United States, celebrate it on the following Sunday.*
"The observance of this feast is of great antiquity. Although no documentary evidence of it exists prior to the beginning of the fifth 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 Sylvia (Peregrinatio Etheriae) 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 (Duchesne, Christian Worship, 491-515). It may be that prior to the fifth 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 fifth century." (Catholic Encyclopedia)
I watched this observance on Canadian TV. I believe the President of the network is the priest.
This service includes "spiritual communion."
It takes a long time for a Protestant (at least for me) to become accustomed to a Catholic mass because all the focus is on the Bible readings and on Jesus, instead of the preacher's sermon (brief) or the music style. However, there is more continuity among these services all over the world than those in our Lutheran church in one location.
*I also watched the Sydney, Australia and Toronto mass. They apparently will be celebrating this on May 8.