In the East, the Festival of the Transfiguration has been celebrated since the late fourth century, and is one of the twelve great festivals of the East Orthodox calendar. In the West it was observed after the ninth century by some monastic orders, and in 1457 Pope Callistus III ordered its general observance.
At the time of the Reformation, it was still felt in some countries to be a "recent innovation," and so was not immediately taken over into most Reformation calendars, but is now found on most calendars that have been revised in the twentieth century. A recent tendency in the West is to commemorate the Transfiguration on the Sunday just before Lent, in accordance with the pattern found in the Synoptics, where Jesus is represented as beginning to speak of his forthcoming death just about the time of the Transfiguration, so that it forms a fitting transition between the Epiphany season, in which Christ makes himself known, and the Lenten season, in which he prepares the disciples for what lies ahead.
Whether observing the Transfiguration then will affect the observation of it on 6 August remains to be seen.