Transferred to Monday, December 9th
2019 is the rare year when the Solemnity of the Immaculate Conception of the Blessed Virgin Mary, the patronal feast of the United States, is not celebrated as a holy day of obligation. Because December 8th falls on the Second Sunday of Advent this year, the Church is moving the solemnity by one day to Monday, December 9th.
The reason? According to the General Norms for the Liturgical Year and Calendar, a Sunday of Advent is ranked higher than a solemnity of the Lord, the Blessed Virgin, Saints in the general calendar, and All Souls; therefore, the Sundays takes precedence over the solemnity.
While the Solemnity of the Immaculate Virgin Mary is being transferred to Monday, the obligation to attend Mass is lifter for the Immaculate Conception.
(GATHERED, A Newsletter from the Office of Worship)