Diagram of the phases of the moon — "This diagram illustrates the Moon’s phases in relation to its distance from the Sun. The Earth at center is surrounded by three concentric rings. Along the inner ring are seven discs showing the phases of the waxing and waning moon, indicated by pale yellow wash emanating from the Sun, at right. As the diagram makes clear, and as medieval authorities recognized, the Moon’s phases are determined by the extent of its illumination by the Sun. The cycle begins with the new, crescent Moon at upper right (approximately 2 o’clock) and moves counterclockwise, with the days of the lunar cycle given in red. It ends when the Moon is not visible -- that is, when it lies directly between the Earth and Sun, the latter labeled 'Sol XXX.' This day was called by Isidore of Seville (d. 636 CE) the “interlunar interval” (Etymologiae III, lv)."

Featured on PDR in the collection Cosmography Manuscript (12th Century)

This wonderful series of medieval cosmographic diagrams and schemas are sourced from a late 12th-century manuscript created in England. Coming to only nine folios, the manuscript is essentially a scientific textbook for monks, bringing together cosmographical knowledge from a range of early Christian writers such as Bede and Isodere, who themselves based their ideas on such classical sources as Pliny the Elder, though adapting them for their new Christian context. As for the intriguing diagrams themselves, The Walters Art Museum, which holds the manuscript and offers up excellent commentary on its contents, provides the following description: