16th-century astronomy. Artwork of Atlas holding up the heavens. This artwork was published in Freiburg in 1503 in the encyclopedia Margarita Philosophica by the German author Gregor Reisch (c.1467-1525). This encyclopedia was very popular, and was one of the standard textbooks of the time. The Earth (behind Atlas) is surrounded by spheres marking the Moon, Mercury, Venus, the Sun, Mars, Jupiter, Saturn, and four outer celestial spheres, the first of which contained the stars. As well as being a geocentric model, this shows Atlas as the universal structure (Macrocosm) that corresponded to the earthly structure (Microcosm) of the human body. This was a central concept in the astrology and natural philosophy of medieval Europe and the Renaissance.