Yes, all three Persons of the Most Blessed Trinity were present at the Transfiguration. St. Thomas Aquinas said, "The whole Trinity appeared: the Father in the voice; the Son in the man; the Spirit in the shining cloud."   All three Synoptic Gospels highlight the Transfiguration (Matthew 17:1–8, Mark 9:2–8, and Luke 9:28–36). This is the account from the Gospel of Luke: Now about eight days after these sayings he took with him Peter and John and James, and went up on the mountain to pray. And as he was praying, the appearance of his countenance was altered, and his raiment became dazzling white. And behold, two men talked with him, Moses and Eli′jah, who appeared in glory and spoke of his departure, which he was to accomplish at Jerusalem. Now Peter and those who were with him were heavy with sleep but kept awake, and they saw his glory and the two men who stood with him. And as the men were parting from him, Peter said to Jesus, “Master, it is well that we are here; let us make three booths, one for you and one for Moses and one for Eli′jah”—not knowing what he said. As he said this, a cloud came and overshadowed them; and they were afraid as they entered the cloud. And a voice came out of the cloud, saying, “This is my Son, my Chosen; listen to him!” And when the voice had spoken, Jesus was found alone. And they kept silence and told no one in those days anything of what they had seen. St. John Paul II said, We, pilgrims on earth, are granted to rejoice in the company of the transfigured Lord when we immerse ourselves in the things of above through prayer and the celebration of the divine mysteries. But, like the disciples, we too must descend from Tabor into daily life where human events challenge our faith. On the mountain we saw; on the paths of life we are asked tirelessly to proclaim the Gospel which illuminates the steps of believers. Likewise, Pope Francis said, From the event of the Transfiguration I would like to take two significant elements that can be summed up in two words: ascent and descent. We all need to go apart, to ascend the mountain in a space of silence, to find ourselves and better perceive the voice of the Lord. This we do in prayer. But we cannot stay there! Encounter with God in prayer inspires us anew to “descend the mountain” and return to the plain where we meet many brothers weighed down by fatigue, sickness, injustice, ignorance, poverty both material and spiritual. To these brothers in difficulty, we are called to bear the fruit of that experience with God, by sharing the grace we have received. According to the Catechism of the Catholic Church, “Christ's Transfiguration aims at strengthening the apostles' faith in anticipation of his Passion: the ascent on to the ‘high mountain’ prepares for the ascent to Calvary. Christ, Head of the Church, manifests what his Body contains and radiates in the sacraments: ‘the hope of glory’” (CCC 568). In both the East and the West the Transfiguration has traditionally been celebrated in August, including on August 6th in many places. In 1456, when tensions were high between Christian Europe and the Ottoman Empire, a major battle was won by Hungary at Belgrade and the Turkish forces defeated, delaying the advance of the Ottomans for seventy years. Word of this victory arrived in Rome on August 6, 1456. As an act of thanksgiving, Pope Callixtus III, who had asked all Christians to pray for victory, named that day as the fixed date for the Church to celebrate the Feast of the Transfiguration.