Feast August 15 : Assumption of Mary into Heaven the Solemnity Remembering when Mary was taken to Heaven - Holy Day of Obligation
Mary, the mother of Jesus, is recorded in the scriptures, the Gospel of Luke, as being "full of grace" and "blessed among women." She was the mother of God, a title given to her by the early church during the council of Ephesus in the year 431 AD. Mary was the closest person to Jesus on earth and carried Him in her womb for 9 months. For centuries, the early church celebrated a feast honoring the death and assumption of Mary into heaven. The solemnity of of the Assumption, celebrated on August 15th, is almost like the church's celebration of Mary's birthday into heaven. In 1950, Pope Pius the 12th infallibly declared that it was a divinely revealed dogma that the Mary the mother of God was assumed body and soul to heaven. Some confuse Mary's assumption with Jesus's ascension, where God ascended to heaven by His own power. (It is a Holy Day of Obligation in the USA and some other countries but due to COVID there is no obligation in many places.)
19 Then God’s temple in heaven was opened, and the ark of his covenant was seen within his temple; and there were flashes of lightning, voices, peals of thunder, an earthquake, and heavy hail. And a great portent appeared in heaven, a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars.
Regarding the day, year, and manner of Our Lady's death, the Church always derived its knowledge of the mystery from Apostolic Tradition. . The belief in the corporeal assumption of Mary is founded on the treatise De Obitu S. Dominae, bearing the name of St. John, which belongs to the fourth or fifth century. It is also found in the book De Transitu Virginis, and in a letter attributed to St. Denis the Areopagite. If we consult genuine writings in the East, it is mentioned in the sermons of St. Andrew of Crete, St. John Damascene, St. Modestus of Jerusalem and others.
St. Juvenal, Bishop of Jerusalem, at the Council of Chalcedon in the year 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.
According to the life of St. Theodosius, who died in 529, it was celebrated in Palestine before the year 500, probably in August.