De revolutionibus orbium coelestium
Gingerich is a recognized authority on both Johannes Kepler and Nicolaus Copernicus, especially in regard to his "De revolutionibus orbium coelestium". He is also an expert on Galileo's astronomical observations, and took a leading role in establishing that the watercolor lunar images in a celebrated copy of Galileo's Sidereus nuncius were modern forgeries and not made by Galileo.