National Catholic Register, Marge Fenelon: We’ve begun the “O” Antiphons.
Every year from December 17-23, the Catholic Church sings what’s known as the “O” Antiphons, the antiphons that accompany the Magnificat canticle of Evening Prayer. They’re called such because each antiphon begins with “O.” You’ll notice them as the Alleluia verse before the Gospel at Mass. The tradition itself dates back to the eighth century. Read more.