Luna (goddess) as Juno Covella, Juno of the crescent moon. Both Juno and Diana were invoked as childbirth goddesses with the epithet "Lucina". Luna is often depicted driving a two-yoke chariot called a "biga", drawn by horses or oxen. In Roman art, the charioteer Luna is regularly paired with the Sun driving a four-horse chariot ("quadriga"). Isidore of Seville explains that the "quadriga" represents the sun's course through the four seasons, while the "biga" represents the moon, "because it travels on a twin course with the sun, or because it is visible both by day and by night—for they yoke together one
Dynamics of the celestial spheres Dynamics of the celestial spheres Ancient, medieval and Renaissance astronomers and philosophers developed many different theories about the dynamics of the celestial spheres. They explained the motions of the various nested spheres in terms of the materials of which they were made, external movers such as celestial intelligences, and internal movers such as motive souls or impressed forces. Most of these models were qualitative, although a few of them incorporated quantitative analyses that related speed, motive force and resistance. In considering the physics of the celestial spheres, scholars followed two different views about the material composition of the celestial spheres.