Here’s a word you may only associate with music: octave. If you have a keyboard, start at middle C and go up the keyboard to the next C. You will sound eight notes in all, from C to C.
In the Church, an octave is the period from Sunday to Sunday, or eight days. The Church understand the octave to represent eternity, or time out of time. Counted in this way, the week begins and ends on the same day, making a circle, a sign of eternity. Counted in this way, Sunday is a day apart from the other days of the week, and so, a taste of eternity. It is a day with its own rhythms and requirements, a day for the wedding of heaven and earth.
In the Church, an octave is the period from Sunday to Sunday, or eight days.
Until the liturgical calendar was reformed in 1969, every Solemnity (the highest feast in the church calendar, such as Christmas) had an octave attached to the actual day. For the most part, now, we keep Solemnities as Holy Days of Obligations, without the additional seven days of celebration. (Christmas still has its octave, culminating in the Solemnity of Mary the Mother of God.)
One of the Holy days of Obligations, which formerly had its own octave, is the Feast of the Assumption on August 15. (Count it: August 15, 16, 17, 18, 19, 20, 21, 22 — eight days.)
Today is the eighth day after the Feast of the Assumption. It is the memorial of the Queenship of the Virgin Mary. Mary was shown great courtesy by God, who would not let the Vessel of Christ suffer death and corruption. She was assumed into heaven, where we honor her today as the Regina Caeli, the Queen of Heaven.
Look at your prayer book. Psalm 45, an ode for a royal wedding, is sung on the feast and on today’s memorial.