3-057-431 - Heritage Art/Heritage Images

Dragon volvelle, 1540. A volvelle, a movable device for finding the places of the planets within the zodiac. A dragon sits in the middle, showing the latitude of the Moon. Its head and tail, caput and cauda, acquired the status of planets in classical astrology. These points were in fact the lunar nodes, the two places where the moon's path crossed the ecliptic each month. The dial gives the position of the nodes through the year. The lunar nodes have been referred to as a dragon's head and tail because of a mythological idea that stated the nodes were dragons which ate the moon or sun. From Astronomicum Caesareum.