A solemnity in the liturgical year is a feast day of the highest rank celebrating a mystery of faith such as the Trinity, an event in the life of Jesus, the Blessed Virgin Mary, or important saints. The observance begins with the vigil on the evening before the actual date of the feast. On these days, both the Gloria and the Creed are recited. 

Feast days in the liturgical year are ranked second in importance and assigned one date out of the year for each and every canonized saint. The saints are remembered on their individual feast days with special mention, prayers, and possibly a scripture reading.  On these weekday Feast Days, the Gloria is said, but not the creed.   There are certain Feast Days that are on Sundays that encourage us to commemorate and celebrate key events in the Life of Jesus.  

At the bottom of the feast-day ladder are memorials, the most common way in which the Church remembers saints and events at Mass and in the Liturgy of the Hours. Memorials may be liturgically “obligatory” – the special two readings and prayers (no Gloria) of the feast day must replace the regular readings and prayers at Mass and in the Liturgy of the Hours – or liturgically “optional,” in which case it’s up to the pastor or celebrant. A Sunday, a solemnity, and a feast (see below) all take liturgical precedence over a memorial.  Only the memorials of those saints who are of “universal significance” are observed by the whole Church and marked in the general liturgical calendar

Holy days of obligation (also known as feasts of precept) are days when the faithful are obliged to participate at Mass and abstain from unnecessary work or other activities which hinder the suitable relaxation of mind and body. Each Sunday is a holy day of obligation, and six Solemnities are also observed as feasts of precept in the United States.  Here you will find the Holy Days of Obligation Mass Times (as soon as they are determined) as well as future dates of Holy Days, Solemnities, and some of the Feast Days.