On April 8, 2013, Catholics will observe the Feast of the Annunciation of the Lord, the celebration of the angel Gabriel's announcement to the Virgin Mary that she had been chosen to be the Mother of God and of the Blessed Virgin's humble acceptance of this honor and responsibility.
Normally, the Feast of the Annunciation falls on March 25, nine months before Christmas. This year, however, March 25 is the Monday of Holy Week, and the Church considers Masses for Palm Sunday, any time in Holy Week, or any time from Easter through the Sunday after Easter (Divine Mercy Sunday) to be so important that even this Marian feast cannot replace one of them. The same is true for the Sundays in Lent. So, when the Annunciation falls on a Sunday in Lent (before Palm Sunday), it is transferred to the following Monday. If it falls on Palm Sunday or any day in Holy Week, it is transferred to Low Monday, the Monday after the Sunday after Easter.
Still, even if the liturgical celebration of the Annunciation has to be transferred, we can observe the traditional date ourselves by reciting the Angelus, an ancient prayer which recounts the angel Gabriel's visit to the Virgin Mary, on March 25. And we can include the Magnificat, the beautiful canticle or biblical hymn that was Mary's response to Gabriel's announcement, as well.
(The Annunciation, Central Russian icon, egg tempera on wood, late 1800's. Photo © Slava Gallery, LLC; used with permission.)