The cover story in the latest issue of Skeptic(1), titled The Art of Imagining UFOs, by Diego Cuoghi, offers a conventional explanation for the strange spaceship-like objects that are sometimes seen in centuries old religious paintings. Cuoghi argues that people who call these UFOs are actually misinterpreting specific symbols that commissioned painters were told to include in their works.
For instance, in this detail from the 15th century painting Miracle of the Snow he says the mysterious aerial objects represent platforms for angels which were routinely used in religious paintings of that period. In the Annunciation, a 15th century painting by Crivelli, Cuoghi says the heavenly vortex and dove are standard devices which were often used in annunciation depictions. And in perhaps the most well known "UFO painting" details from a 16th century Crucifixion fresco, are not portraying ET craft but the sun and the moon, which were often presented with a human face, he writes.To view a gallery of more of these types of images, and get the less skeptical point of view, check out Matthew Hurley's ufoartwork.com(2).