1.8 The moon

Although Aristotle's natural philosophy was very influential in the Greek world, it was not without competitors andskeptics. Thus, in his little book On the Face in the Moon's Orb , the Greek writer Plutarch (46-120 CE) expressed rather different views on the relationship between theMoon and Earth. He suggested that the Moon had deep recesses in which the light of the Sun did not reach and that the spots arenothing but the shadows of rivers or deep chasms. He also entertained the possibility that the Moon was inhabited. In thefollowing century, the Greek satirist Lucian (120-180 CE) wrote of an imaginary trip to the Moon, which was inhabited, as werethe Sun and Venus.

The medieval followers of Aristotle, first in the Islamic world and then in Christian Europe, tried to make sense of the lunarspots in Aristotelian terms. Various possibilities were entertained. It had been suggested already in Antiquity that theMoon was a perfect mirror and that its markings were reflections of earthly features, but this explanation was easily dismissedbecause the face of the Moon never changes as it moves about the Earth. Perhaps there were vapors between the Sun and the Moon,so that the images were actually contained in the Sun's incident light and thus reflected to the Earth. The explanation thatfinally became standard was that there were variations of "density" in the Moon that caused this otherwise perfectlyspherical body to appear the way it does. The perfection of the Moon, and therefore the heavens, was thus preserved.

It is a curious fact that although many symbolic images of the Moon survive in medieval and Renaissance works of art (usually acrescent), virtually no one bothered to represent the Moon with its spots the way it actually appeared. We only have a few roughsketches in the notebooks of Leonardo da Vinci (ca. 1500) and a drawing of the naked-eye moon by the English physician William Gilbert . None of these drawings found its way into print until well after the telescope had come into astronomy.