Defaulting to perfection

A 9th-century diagram of the Ptolemaic system with Earth at the centre, then the Moon (Luna), Sun (Sol), Mercury, Venus, Mars, Jupiter and Saturn, St. Gallen, Stiftsbibliothek, Cod. Sang. 248

The myth that medieval people thought the Earth was flat has long been debunked. Nevertheless, it persists in the imagination of many today. Periodically, popular …