Solemnity of Pentecost: 50 days after Easter.
Pentecost is the last day of the Easter Season.
Solemnity of the Most Holy Trinity: Sunday after Pentecost
Solemnity of the Body and Blood of Christ: 2nd Sunday after Pentecost
Solemnity of the Assumption of the Blessed Virgin Mary into Heaven: August 15
Solemnity of All Saints: November 1
Information is from Catholic Encyclopedia at New Advent
The rhythm of the liturgical seasons reflects the rhythm of life — with its celebrations of anniversaries and its seasons of quiet growth and maturing.
Ordinary Time, meaning ordered or numbered time, is celebrated in two segments: from the Monday following the Baptism of Our Lord up to Ash Wednesday; and from Pentecost Monday to the First Sunday of Advent. This makes it the largest season of the Liturgical Year.
In vestments usually green, the color of hope and growth, the Church counts the thirty-three or thirty-four Sundays of Ordinary Time, inviting her children to meditate upon the whole mystery
of Christ – his life, miracles and teachings – in the light of his Resurrection.
If the faithful are to mature in the spiritual life and increase in faith, they must descend the great mountain peaks of Easter and Christmas in order to "pasture" in the vast verdant meadows of tempus per annum, or Ordinary Time.
Sunday by Sunday, the Pilgrim Church marks her journey through the tempus per annum as she processes through time toward eternity.
For a penetrating look at how the seasons of the year interlock with the seasons of our lives read Dr. Jeffrey Mirus' article Seasons: The Lesson of Life.
From Catholic Culture.org