Because the Second Sunday of Advent takes precedence over other feast days, the Solemnity of the Immaculate Conception of the Blessed Virgin Mary (Dec. 8) will be observed Monday, Dec. 9, this year, according to Julie Grace Males, director of the Office of Worship for the Archdiocese of Baltimore.
Catholics are encouraged, but not obligated to attend Mass that day, celebrating the dogma that Mary was preserved from original sin from the moment of her conception. As with all Sundays, Catholics are obligated to attend Mass on the Second Sunday of Advent.
In 1846, while meeting in Baltimore, the U.S. bishops adopted a decree naming Mary, “conceived without sin,” as patroness of the United States. Pope Pius IX approved the choice and placed the United States under the patronage of the Immaculate Conception in 1857.