The Assumption of Mary

 The feast of the Dormition of the Theotokos is celebrated on August 15 (in the West, this is known as the Feast of the Assumption). 

From the Greek Orthodox: The Feast of the Dormition of Our Most Holy Lady, the Theotokos and Ever-Virgin Mary is celebrated on August 15 each year. The Feast commemorates the repose (dormition and in the Greek kimisis) or "falling-asleep" of the Mother of Jesus Christ, our Lord. The Feast also commemorates the translation or assumption into heaven of the body of the Theotokos. Information on the Icon of the Feast.

A line drawing of the Icon for coloring is found on pg. 5. 

According to New Advent Catholic Encyclopedia, nothing is known for certain of Our Lady's death. Pious tradition is that she died between three and fifteen years after Our Lord's resurrection, and she was surrounded by the remaining apostles save Thomas who did not make it back from India in time. St. John of Damascus (P.G., I, 96) thus formulates the tradition of the Church of Jerusalem:

St. Juvenal, Bishop of Jerusalem, at the Council of Chalcedon (451), made known to the Emperor Marcian and Pulcheria, who wished to possess the body of the Mother of God, that Mary died in the presence of all the Apostles, but that her tomb, when opened, upon the request of St. Thomas, was found empty; wherefrom the Apostles concluded that the body was taken up to heaven.

Further from New Advent: 

By promulgating the Bull Munificentissimus Deus, 1 November, 1950, Pope Pius XII declared infallibly that the Assumption of the Blessed Virgin Mary was a dogma of the Catholic Faith.