The octave isn't just found in music, it's also found in liturgy
https://en.wikipedia.org/wiki/Octave_(liturgy)
There are many octaves in liturgy, but the only ones still in practice (that i know of) are:
Octave of Easter - https://en.wikipedia.org/wiki/Octave_of_Easter
Octave of Christmas - https://en.wikipedia.org/wiki/Octave_of_the_Nativity
I started studying octaves in liturgy when i came across the octave of the assumption; there were two notable feast days and one notable rosary recitation during this octave period ...
(1) first day: assumption - https://en.wikipedia.org/wiki/Assumption_of_Mary
(4,5) midweek: immaculate heart of mary rosary - https://en.wikipedia.org/wiki/Immaculate_Heart_of_Mary
(8) last day: queenship - https://en.wikipedia.org/wiki/Queen_of_Heaven
Circle of Stars
Madonna in Glory, c. 1670, oil on canvas by Carol Dolci
Wikipedia Commons
my personal feeling about it, is that it pertains to octave musical language and the eight day concept in Catholicism ...
eight notes in a musical octave is some what different than the eight echio in a musical system because of the octave species is a special music system within the entire music system
Octoechos - https://en.wikipedia.org/wiki/Octoechos
Octoechos in Liturgy - https://en.wikipedia.org/wiki/Octoechos_(liturgy)
From the Catholic Catechism:
CCC 2174 Jesus rose from the dead "on the first day of the week."104 Because it is the "first day," the day of Christ's Resurrection recalls the first creation. Because it is the "eighth day" following the sabbath,105 it symbolizes the new creation ushered in by Christ's Resurrection. For Christians it has become the first of all days, the first of all feasts, the Lord's Day (he kuriake hemera, dies dominica) Sunday:
- We all gather on the day of the sun, for it is the first day [after the Jewish sabbath, but also the first day] when God, separating matter from darkness, made the world; and on this same day Jesus Christ our Savior rose from the dead.106
Helmholtz octave name system
there is a lot to music; check out harp music at http://sites.siba.fi/en/web/harpnotation/octave-names
