Depending on what calendar you follow, and/or where you live, this Sunday is either Sunday after the Ascension, the feast of the Ascension, or Sunday in the Octave of the Ascension.
The feast of the Ascension itself of course occurred last Thursday, consistent with Scripturally specified number of days following the Resurrection. But the external solemnity is moved to this Sunday in many countries.
So far as the Office goes, prior to 1962, the feast had an octave, so the remnants of that are used to provide a distinct flavour to these nine days, even though the Octave itself has been abolished.
The Office this week in the 1962 Benedictine calendar
Sun 12 May Sunday after the Ascension, Class II; SS Nereus, Archilleus and Pancras,
Mon 13 May Class IV; St Robert Bellarmine, Memorial
Tues 14 May Class IV; St Pachomius, Memorial
Wed 15 May Class IV
Thurs 16 May Class IV
Fri 17 May Class IV
Sat 18 May Whitsun Eve (Vigil of the Pentecost), Class I