CREEPYPASTA RUSSIAN EXPERIMENT
Icon of the Transfiguration by Theophanes the Greek, 15th century
The Feast of the Transfiguration of Jesus is celebrated by various Christian denominations. The origins of the feast are less than certain and may have derived from the dedication of three basilicas on Mount Tabor.  The feast was present in various forms by the 9th century, and in the Western Church was made a universal feast on August 6th by Pope Callixtus III to commemorate the raising of the Siege of Belgrade (1456). 
In the Syriac Orthodox, Indian Orthodox, Revised Julian calendars within Eastern Orthodoxy, Roman Catholic, Old Catholic, and Anglican churches, the Feast of the Transfiguration is observed on 6 August. In those Orthodox churches which continue to follow the Julian Calendar, August 6 falls on August 19 of the Gregorian Calendar. The Transfiguration is considered a major feast, numbered among the twelve Great Feasts in Orthodoxy. In all these churches, if the feast falls on a Sunday, its liturgy is not combined with the Sunday liturgy, but completely replaces it.
In some liturgical calendars (e.g. the Lutheran and United Methodist) the last Sunday in the Epiphany season (that immediately preceding Ash Wednesday) is also devoted to this event. In the Church of Sweden and the Church of Finland, however, the Feast is celebrated on the seventh Sunday after Trinity, the eighth Sunday after Pentecost.
The Old Catholic Church celebrates the Transfiguration typically on August 6, according to the Roman rite calendar; however, every local Old Catholic Church throughout the world has the option to celebrate this major feast on a different day. The Old Catholic theological view of the Transfiguration shares much in common with the Eastern Orthodox perspective as stated above. Old Catholics also believe that the transfiguration was a major event that revealed the divinity of Christ; that Jesus is indeed the splendor and eikon of the Father. The Transfiguration shows forth humanity in the splendor of its original form when it was united in the life-giving love of the Triune God. This event reveals the possibility of humanity’s theosis.
If the Transfiguration falls on a Sunday, it replaces the ordinary liturgical Ordo of the season for Sacred Liturgy.
In the Roman Catholic Church, the Transfiguration was once celebrated locally in various parts of the Catholic world on different days, including August 6, but was not universally recognized. In 1456, the Kingdom of Hungary repulsed an Ottoman invasion of the Balkans by breaking the Siege of Belgrade. News of the victory arrived in Rome on August 6.  Given the importance to international politics at that time of such battles between Christian and Muslim nations, in celebration of the victory Pope Callixtus III elevated the Transfiguration to a Feast day to be celebrated in the entire Roman rite.
In 2002, Pope John Paul II selected the Transfiguration as one of the five Luminous Mysteries of the rosary.
The Evangelical Lutheran Church in America observes the Feast of the Transfiguration as the last Sunday after the Epiphany, which is the Sunday immediately preceding Ash Wednesday and the season of Lent.