These days are Holy Days of Obligation.
Solemnity of Mary, Mother of God – January 1
Assumption of the Blessed Virgin Mary – August 15
All Saints' Day – November 1
Feast of the Immaculate Conception – December 8
Christmas – December 25
In addition, all Sundays of the year are considered holy days of obligation, because the faithful are always called to attend Mass on Sunday.
If a Holy Day falls on the day before, or the day after, a Sunday, the obligation to attend Mass is cancelled, but Epiphany always offers Mass on those days since they remain Holy Days even if not “of obligation.”
If any of these days except for Immaculate Conception fall on a Sunday, then the Holy Day is observed instead of whatever other liturgical observance is prescribed for the day.
If Immaculate Conception falls on a Sunday, it is transferred to the following Monday.
The Solemnity of Epiphany, as the patronal feast of the Parish, is a special day of solemnity, as is the Solemnity of the Dedication of Epiphany Church, observed each year on a Sunday around the end of June.