Copley's Ascension is closely modeled after Raphael's Transfiguration, which he considered one of the greatest paintings of the Renaissance.

Left: John Singleton Copley, The Ascension, 1775, oil on canvas, The Museum of Fine Arts, Boston. Photograph © 1996 The Museum of Fine Arts, Boston.
Right: Raphael, Transfiguration. Pinacoteca, Vatican Museums, Vatican State. Scala/Art Resource, NY.