Image Credit (CC BY-SA 4.0)
From the Peterskirche, Vienna, Austria
June 2014 was like this June: packed with Solemnities. Homiletic & Pastoral Review ran this article of mine a year later when it was almost true:
This June is a very solemn month. There are six solemnities on the liturgical calendar: Pentecost Sunday, Trinity Sunday, Corpus Christi, the Sacred Heart of Jesus, the Nativity of St. John the Baptist, and Sts. Peter and Paul, Apostles. The first four are movable feasts, scheduled according to the date of Easter each year: Pentecost Sunday, 50 days after Easter, Trinity Sunday, a week after Pentecost Sunday; Corpus Christi, the Thursday after Trinity Sunday (usually moved to the Sunday following, in the U.S.); and the Sacred Heart of Jesus, the Friday after Corpus Christi. The Birth of St. John the Baptist is a fixed feast: June 24th. In Quebec, his feast is celebrated with parades and festivities since he is the patron saint of that Canadian province. The Solemnity of Sts. Peter and Paul is on June 29 . . .
For those who celebrated Ascension Thursday on Ascension Sunday, there were actually seven!
Because this year the Solemnity of Sts. Peter and Paul, being fixed on June 29 and the Solemnity of the Sacred Heart of Jesus--being a movable feast, based on the movable Solemnity of Corpus Christi, which is scheduled based on the date of Easter Sunday every year--is on June 28, we do not celebrate the Memorial of the Immaculate Heart of Mary this year. It would usually be on the Saturday after the Solemnity of the Sacred Heart.
This is one of those orderly and hierarchical elements of Catholicism: there are distinctions between how we celebrate certain days. If you attend daily Mass with any regularity on these days you see the difference.
Solemnities are the highest level of celebration: at Mass, we'll sing or recite the Gloria and the Nicene Creed, and there are three readings--just like a Sunday Mass. We begin the celebration of Solemnities the evening before with Vespers in the Divine Office. The readings are specific to the Solemnity and the other Propers highlight the celebration. Solemnities are often Holy days of Obligation.
Feasts are the next highest level: at Mass we'll sing or recite the Gloria but not the Creed and there is no vigil. (Except for the Feast of the Presentation!) Some readings will be required during Mass; for example, when the Feast celebrates an Apostle, a reading from the New Testament that mentions the saint will be obligatory; there are just two readings (Epistle and Gospel): Except for the Feast of the Presentation! It's an exceptional feast! When February 2 occurs on a Sunday the Feast of the Presentations takes precedence. (Perhaps it should be called a Solemnity?)
Memorials and optional memorials of saints are the next level: usually the Collect and other prayers mention the saint, but the readings are part of the cycle in the Lectionary. An optional memorial is just that: it is optional whether or not it is celebrated.
On some days, there is more than one memorial to choose from, like January 23: Saint Vincent, Deacon and Martyr or Saint Marianne Cope, Virgin; February 8: Saint Jerome Emiliani or Saint Josephine Bakhita, Virgin; May 25: Saint Bede the Venerable, Priest and Doctor of the Church or Saint Gregory VII, Pope or Saint Mary Magdalene de’Pazzi, Virgin, etc. The priest may decide whom to commemorate according to the devotion of the parish.
As this website summarizes it:
For complete details on the order of precedence, please consult the General Norms for the Liturgical Year and the New General Roman Calendar issued by Pope Paul VI in 1969. Nevertheless, the basic rule of thumb is this: Sundays, other Solemnities, Holy Week, and the Octave of Easter always take precedence. These are followed by Feasts, weekdays of Advent (December 17-24), days within the Octave of Christmas, weekdays of Lent, obligatory memorials, optional memorials, weekdays of Advent (through December 16), other weekdays of the Christmas Season, other weekdays of the Easter Season, and weekdays in Ordinary Time.
Notice also from that website that religious communities, dioceses and even countries can celebrate a saint's memorial as a feast:
Particular churches, countries, or religious communities may also celebrate the memorials of other saints of “special significance” in accord with their special devotions. For example, the memorial in honor of the patron saint of a diocese is raised to a “feast.”
In the USA, for example, June 22 is the Memorial of Saints John Fisher and Thomas More. In England, it's a Feast!
Note on the Calendar for England and Wales, the Solemnity of Sts. Peter and Paul was moved to Sunday, June 30 so that the memorial of the Immaculate Heart of Mary is celebrated today on Saturday, June 29.
Those "weekdays" when there is no memorial or feast to celebrate are also called ferial days, as this website explains:
In the revised liturgical calendar, a weekday on which no special feast or vigil is celebrated in the Mass or the Liturgy of the Hours. On ferial days the Mass may be that of the preceding Sunday, or an optional memorial, or a votive Mass, or a Mass for the deceased. During Advent and Lent ferial days are in a privileged category, and the same freedom in the choice of Masses is not allowed. In general, the Mondays through Fridays of each week are called ferial days (feriae) and are counted, in sequence, from two to six. Sunday, or the Lord's Day (Dominica), is always the first day, and Saturday (Sabbatum) is the seventh day of the week.
Feria means "free day"! On a ferial day, a priest may choose to celebrate a Votive Mass, like celebrating the Votive Mass of the Sacred Heart of Jesus on a ferial Friday.
For each liturgical year, the United States Conference of Catholic Bishops publishes a calendar that contains notes about which feasts or memorials are celebrated and which aren't. For example:
7. Since the Solemnity of the Most Sacred Heart of Jesus is celebrated on June 28, 2019, the Memorial of Saint Irenaeus, Bishop and Martyr, is omitted this year.8. Since the Solemnity of Saints Peter and Paul, Apostles, is celebrated on June 29, 2019, the Memorial of the Immaculate Heart of the Blessed Virgin Mary is omitted this year.9. Since December 8, 2019, is the Second Sunday of Advent, the Solemnity of the Immaculate Conception of the Blessed Virgin Mary is transferred to Monday, December 9, 2019. The obligation to attend Mass, however, does not transfer. The Optional Memorial of Saint Juan Diego Cuauhtlatoatzin, December 9, is omitted this year.
In spite of these variations, however, in her private devotions, any Catholic may observe a saint on his or her feast day.
So: Immaculate Heart of Mary, pray for us!