Today is the Feast of the Immaculate Conception, a holy day of obligation. The solemnity of the Immaculate Conception celebrate Mary's conception without sin. The day does not refer to the conception of Jesus in the womb of Mary but rather the conception of Virgin Mary in the womb of Saint Anne by Mary's father St. Joachim. Her conception was immaculate as she was filled with grace by God who knew that she will become the mother of our Savior, Jesus Christ. Exactly 9 months later, we celebrate Mama Mary's birthday on September 8.
On December 8, 1854, Pope Pius IX declared the Immaculate Conception a dogma of the church. As written in the Apostolic Constitution Ineffabillis Deus, "We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Saviour of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful."