We now enter Christmastide, which includes the Christmas Season followed by the Season of Epiphany.
The first 8 days of the Christmas Season is known as the Octave of Christmas. It starts with Christmas on December 25th and ends with the Solemnity of Mary, the Mother of God on January 1st.
The Christmas Season continues on from the 1st, ending with the Epiphany of the Lord, which is the first Sunday after the Solemnity of Mary, Mother of God, so the Christmas Season may be as short as 9 days, and as long as 15.
Christmastide continues from Epiphany and concludes with the Baptism of the Lord, the Sunday following Epiphany. This period is the Season of Epiphany.
Christmastide is rich with Feast Days and Solemnities:
In December:
25th - Solemnity of the Nativity of the Lord
26th - St. Stephen, the First Martyr
27th - St. John, Apostle and Evangelist
28th - Feast of the Holy Innocents
29th - Feast of the Holy Family of Jesus, Mary and Joseph
In January:
1st - Solemnity of Mary, the Mother of God
3rd - Memorial of The Most Holy Name of Jesus
5th - Solemnity of the Epiphany of the Lord
12th - Feast of the Baptism of the Lord
Octave of Christmas:
Cooperation with God's Grace