The Almagest

A historian has discovered that a 16th-century printed edition of the Almagest — an ancient and influential astronomical treatise — includes numerous handwritten footnotes by Galileo Galilei, the astronomer who later challenged the geocentric view of the universe presented in that treatise. Courtesy of the National Central Library of Florence.

A copy of Ptolemy's Almagest with notes in Galileo's handwriting was discovered in Florence.

Researchers have identified numerous notes attributed to Galileo in a 16th-century copy of Ptolemy's central astronomical work, a discovery that may shed new light on how he evolved from the geocentric tradition to the revolution.