The 15th of September is the Feast day of Our Lady of the Seven Dolors.

Also know as the feast day of Our Lady of Sorrows

What are the specific "seven sorrows" of Mary, and why does the Church encourage our liturgical and personal meditation upon these sorrows?

The specific number of sorrows, originally varied, became fixed to these seven events:
1) Simeon's prophecy in the temple
2) the flight of the Holy Family into Egypt
3) the loss of the Christ child in the temple
4) the encounter of Mary with Jesus on the way of the cross
5) the crucifixion and death of Jesus
6) the taking down of Jesus from the cross
7) the burial of Jesus in the tomb.

The Stabat Mater, the medieval sequence recited on this memorial, reminds us:

Can the human heart refrain
From partaking in her pain,
In that Mother's pain untold?

Let me share with you this pain
Who for all our sins was slain,
Who for me in torments died.

from Zenit