Please note - Whenever January 1, the solemnity of Mary, Mother of God, or August 15, the solemnity of the Assumption, or November 1, the solemnity of All Saints, falls on a Saturday or on a Monday, the obligation to attend Mass is lifted.
Solemnity of Mary, January 1
This feast, closely connected to the feast of Christmas, is the most important and oldest of the major feasts of Mary. Mary's Divine Maternity became a universal feast in 1931. Liturgical reform initiated by Vatican II placed it on January 1 in 1969. Prior to this, this feast celebrated on January 1 was the circumcision of Jesus.
As a conference, the U.S. bishops decided, with Vatican approval given July 4, 1992, that when the solemnities of Mary, the Mother of God (January 1), the Assumption (August 15) or All Saints (November 1) fall on a Saturday or Monday, it is not an obligation to attend Mass for these feasts.
Although the obligation to attend when these three holy days fall on a Saturday or Monday is abolished, parishes are to continue to observe these Holy Days by scheduling one or more Masses at a convenient time so that people who wish to participate are able to do so.
Assumption of the Blessed Mother, August 15
This is the principal feast of Mary. It has a double purpose: first, the happy departure of Mary from this life and second, the assumption of her body into heaven.
Little for certain is known about the day, year and manner of Mary's death. The dates assigned for it vary between three and fifteen years after Jesus' Ascension.
All Saints' Day, November 1
This feast honors all the saints, known and unknown.
This feast was first celebrated on May 13, 610, when Pope Boniface IV proclaimed the day Feast of All Holy Martyrs in Rome. The intent was to honor all martyrs who were not included in local records. In 835, Pope Gregory IV changed the date and name to November 1 and Feast of All Saints. A fall date allowed people to celebrate with food from the fall harvest.
Immaculate Conception of Mary, December 8
The Immaculate Conception of Mary, the Mother of Jesus, is the belief that God preserved Mary from any inclination to sin, the inheritance of original sin passed on to all mankind from Adam and Eve.
The feast of the Conception of Mary appeared in the Roman calendar in 1476. After the dogmatic definition by Pope Pius IX in 1854, it became the Feast of the Immaculate Conception.
Christmas, December 25
This feast, one of the two major feast of the liturgical year, celebrates the birth of Jesus.