It is also the day on which the Immaculate Conception of the Blessed Virgin is normally celebrated.
In the new calendar, the Feast of Our Lady gives way to the Sunday; so the Feast is celebrated tomorrow.
I understand the idea, I really do. But the reality is different. Who will go to Mass tomorrow to celebrate the Feast? I would love to - but there is no Mass in our Parish Church tomorrow. I am sure that is true elsewhere, and I am also sure that even when there is a Mass tomorrow, the numbers attending will be far smaller than today's.
So the net result is that most of us will miss out on the Mass for this Feast: and that seems to me to be a shame.
In the traditional rite calendar, the Feast is celebrated, with a commemoration of the Sunday, too. So it is quite legitimate to celebrate the feast today, at home.
Here is the collect for the Second Sunday of Advent, in the Extraordinary Form:
Excita, Dómine, corda nostra ad præparándas Unigéniti tui vias: ut per ejus advéntum, purificátis tibi méntibus servíre mereámur.
Stir up our hearts, O Lord, to make ready the ways of thine only-begotten Son; and with minds undefiled to pay to thee the homage of our service.
This is the prayer we say around our Advent Wreath for the whole of this week.
And here is a recording of the Chant Offertory for today's feast in the Extraordinary Form.
Ave Maria, gratia plena, Dominus tecum. Benedicta tu in mulieribus. Alleluia.
Hail Mary, full of grace, the Lord is with thee; blessed art thou amongst women, alleluia.