We are in the midst of yet another octave, the third in four weeks and the first, depending on which kalendar you use, of four in the coming weeks. June is a celebratory month in contrast to the starkness of the following month of July, perhaps intended by the Church as a gradual easement into green season after the timely joy of Paschaltide.
The octave we now hold, that of Corpus Christi, is generally like most other octaves in the traditional kalendar and somewhat unlike the three retained in the 1962 kalendar. The Mass and Office are repeated every day that is not a feast of nine lessons, and the octave is commemorated when such a feast does fall within the octave. On the eighth day the Mass is resumed with solemnity and no unnecessary commemorations and the Office returns to a Duplex formula. It concludes the festivity by re-iterating the feast itself in most cases, although there are exceptions such as the unique Mass on the Octave Day of Ss Peter & Paul, retained in the 1962 Missal at least as a votive Mass of the Saints.
Our three most unique octaves, however, which survived Papa Pacelli's scissors, really do not follow this pattern very well at all. Pascha and Pentecost admit no feasts whatsoever. The Nativity octave need not concern itself with this since it is already both de tempore and sanctoral. What is most extraordinary is that their octave days resemble the feast very little.
White Sunday is a privileged Double with the Dominical Office of 18 Mattins psalms, the return of hymnody, no Victimae paschali laudes at Mass, and no Alleluia appended to the dismissals. At first glance it might appear that the Holy Saturday Mass and is in fact more Paschal than the Paschal Octave Day. In fact in these eldest rites the eighth day marks a point of departure in bringing the character of the feast back into normality. By contrast, the Holy Saturday Mass anticipated the Resurrection without explicitly making it present.
In a like manner, the last day of the Christmas octave synthesizes the Nativity of Christ, the Circumcision, and the motherhood of Our Lady. The Office is completely different from that of the preceding Nativity days and those of the comites Christi, instead following the psalmnody of a Marian feast. Only the collect of Mass, however, reflects this Marian character. The Introit is that of the third Mass of Christmas day, but the readings are of Christ's circumcision. The hymns are not those of the Nativity itself, but the purpose of the feast is clearly the end of celebration of His birth.
Pentecost does not appear to have a proper octave day, although Trinity Sunday could reasonably be considered a crowning point of the Holy Spirit, the fullness of the life-giving Trinity now revealed and manifested. The compunction of Alleluias from Paschaltide is gone as is the Regina coeli. Indeed, the Byzantine rite also ends its Pentecost—on Sunday—with a transition back to normality with "kneeling" Vespers, reviving the prostrations in the Office and after the epiclesis during the Liturgy. And yet in the Byzantine rite the week following Pentecost is not an official extension of the feast, but it is called Trinity Week and fasting is banned.
Perhaps those Orientalizing, archaeologizing vitiations weren't so wise after all?