The feast of the Nativity of the LORD is a double feast with an Octave and its liturgical colour is white.
At Vespers yesterday afternoon the antiphons Rex pacificus magnificatus est etc were sung with psalms 109, 110, 111, 112 & 113. The Office hymn was Christe Redemptor omnium. At Compline, and the Hours throughout the Octave, a proper Doxology, Gloria tibi Domine, Qui natus es de Virgine, Cum patre et almo Spiritu, In sempiterna saecula, is sung at all hymns of Iambic metre until the Epiphany.
At Mattins the invitatory is Christus natus est nobis, Venite adoremus. When intoning the hymn, Christe, Redemptor omnium, the Hebdomadarius turns and bows to the altar. Mattins has three nocturns and the usual nine lessons. In the first nocturn the lessons are from Isaiah but, interestingly, are sung without a title. These are the same as in the modern editions. In the second nocturn the lessons are taken from a homily on the Nativity by St. Leo. All three lessons are longer than in the post-Clementine editions. In the third nocturn three Gospel pericopes are sung, two from St. Luke and the third from St. John. The seventh lesson does not begin at the words Quia, largiente Domino, as in the later editions, but at Quid est, quod nascituro Domino. It is longer by a couple of sentences. The eighth lesson is longer by a sentence and the ninth lesson by several sentences. After the Te Deum the collect is sung followed by Benedicamus Domino. Then the first of the three Masses for the Nativity is sung. The Gloria is sung (one theory of its origin in the Mass rite is from the song of the Angels on Christmas night to the shepherds) as is the Creed. The preface and communicantes are of the Nativity. Lauds immediately follow this Mass.
At Lauds a different set of antiphons to those used at first Vespers, Quem vidistis pastores etc., are sung with the Dominical psalms (92, 99, 62-66, Benedicite, 148-149-150). The Office hymn is A solis ortus cardine.
Later in the morning Prime is sung. The first antiphon from Lauds, Quem vidistis pastores, is sung with the festal psalms (53, 118i & 118ii). In the short responsory the versicle Qui natus es de Maria Virgine is sung. Prime is followed by the second Mass, the Missa in aurora, that has a second collect to commemorate St. Anastasia. The Gloria and Creed are sung, the preface and communicantes are of the Nativity.
After Terce the third Mass is sung. This Mass too has the Gloria and Creed along with the preface and communicantes of the Nativity. As the Gospel pericope for this Mass is In principio the Gospel of the Epiphany, Cum natus esset Jesus, is read as a proper last Gospel.
Second Vespers has yet a third set of proper antiphons for the feast, Tecum principium etc., that are sung with psalms 109, 110, 111, 129 and 131. These antiphons and psalms will be used through the Octave. After the collect of the feast a commemoration is sung of the following feast of St. Stephen.
A very blessed and Holy, Julian Kalendar, Christmass to all.