The feast of the Nativity of the LORD is a Double of the First Class with a privileged Octave of the third order. The liturgical colour of the feast is white.
Mattins is ordinarily sung later in the evening than usual, so that the Mass which immediately follows can begin at midnight. The Caeremoniale Episcoporum gives special instructions, Lib.II, Cap. XIV, 3, for Pontifical Mattins, but may be reasonably applied to other celebrations or arranging adequate candles to supply light for the service and talks of candelabris ferreis magnis to help provide this. One can easily see where the modern practice of candlelit nine lessons and carols comes from, but how unfortunate that the same effort is not made to celebrate solemn Mattins! The invitatory is proper, Christus natus es nobis: Venite adoremus. When intoning the hymn, Jesu, Redemptor omnium, the Hebdomadarius turns and bows to the altar. Mattins has three nocturns and the usual nine lessons. In the first nocturn the antiphon Dominus Dixit etc are sung with psalms 2, 18 & 44. The lessons are from Isaiah but, interestingly, are sung without a title. In the second nocturn the antiphons Suscepimus etc are sung with psalms 47, 71 & 84. The lessons in the second nocturn are taken from a homily on the Nativity by St. Leo. In the third nocturn the antiphons Ipse invoccabit etc are sung with psalms 88, 95 & 97. The lessons are three Gospel pericopes, two from St. Luke and the third from St. John. 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 Mass. The antiphons Quem vidistis pastores etc are sung the Dominical psalms. The Office hymn is A solis ortus cardine.
Later in the morning Prime is sung. All hymns of Iambic metre have the tone and Doxology in honour of the Incarnation, Jesu tibi sit gloria etc. 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. The lectio brevis is Ipsi peribunt. Prime is followed by the second Mass, the Missa in aurora. In the second Mass the Gloria is sung, there is a second collect to commemorate St. Anastasia. The Creed is sung and 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. The following feast of St. Stephen is commemorated. At Compline the Dominical psalms are sung.
In the 'liturgical books of 1962' at Mattins in the third nocturn, and for the Octave, psalm 88, Misericordias Domini is cut from 51 to 36 verses. The verses from Tu vero repulisti et despexisti to the end are omitted. The tone and Doxology in honour of the Nativity is not sung at the hymns of the Little Hours. In the third Mass the last Gospel is omitted and at Vespers no commemoration of St. Stephen is made.
A very blessed and Holy Christmass to all.