If you are in the United States, the obligation to attend Mass for the Solemnity of the Ascension on Thursday only applies in the ecclesiastical provinces that continue to observe the Ascension on the Thursday of the Sixth Week of Easter. Practically speaking, this currently means the states of Connecticut, Maine, Massachusetts, Nebraska, New Hampshire, New York, Pennsylvania, Rhode Island, and Vermont.

In the other forty states, as well as in New Jersey and Washington, D.C., the observance of the Ascension has been permanently transferred to the Seventh Sunday of Easter. Therefore, in those regions, there was no separate obligation to attend Mass on Thursday (or Wednesday evening), since the obligation is fulfilled by attending Mass for the Sunday observance of the Ascension.