The Solemnity of Mary Mother of God commemorates the divine motherhood of the Blessed Virgin Mary, the God-Bearer, Mother of our Lord and God Jesus Christ. It is celebrated on January 1st, one week after Christmas
The origins of a feast celebrating Mary's divine maternity are obscure, but there is some evidence of ancient feasts commemorating Mary's role as theotokos. Around 500 AD the Eastern Church celebrated a "Day of the Theotokos" either before or after Christmas. This celebration eventually evolved into a Marian feast on December 26th in the Byzantine calendar and January 16th in the Coptic calendar. In the West, Christmas has generally been celebrated with an octave, an eight day extension of the feast. The Gregorian and Roman calendars of the 7th century mark the Christmas octave day with a strong Marian emphasis. However, eventually in the West, the eighth day of the octave of Christmas was celebrated as the Feast of the Circumcision of Jesus. The push for an official feast day celebrating Mary's divine maternity started in Portugal, and in 1751 Pope Benedict XIV allowed Portugal's churches to celebrate Mary's divine maternity on the first Sunday in May. The feast was eventually extended to other countries, and by 1914 was being celebrated on October 11. The feast of Mary's divine maternity became a universal feast in 1931.
However, following Vatican II, Pope Paul VI decided to change the feast of Jesus' Circumcision to the Solemnity of Mary Mother of God to reclaim the ancient Western Marian emphasis at the end of the Octave of Christmas. Celebrating Mary's divine maternity during the Christmas octave makes complete sense in that the celebration is connected closely to Christ's birth...
Prayer to Mary Mother of GodWe fly to thy patronage,
O holy Mother of God;
despise not our petitions in our necessities,
but deliver us always from all dangers,
O glorious and blessed Virgin. Amen.
Third Century; Oldest Known Prayer to Mary