Now it came to pass, when all the people were baptized, that when Jesus was also being baptized and was praying, heaven was opened; and the Holy Ghost descended in a bodily shape, as a dove, upon him; and a voice came from heaven: "Thou art my beloved Son; in thee I am well pleased." [Luke 3: 21-22]It is no wonder that so many beautiful works of art have been made commemorating this glorious revelation of the Blessed Trinity: God the Father speaks of His beloved Son and the Holy Spirit descends upon that incarnate Son, Jesus Christ. What a scene!
Here is Bartolome Esteban Murillo's painting of the event (this is also the image I included in the Sacred Art Series' The Holy Gospels of St. Luke and St. John.
Murillo was a Spanish baroque painter and has become one of my favorites. Here is his wikipedia page; many of his paintings are available at wikiart.org here.