First published in 1543, Nicholas Copernicus’ De revolutionibus orbium coelestium introduced the world to the concept of a sun-centered universe. In it, Copernicus detailed how the motions of the sun, moon, planets, and stars could be explained if the earth orbited the sun — a revolutionary idea. Starting in the 1970s, researcher Owen Gingerich began surveying all known copies of this work from its first two printings in 1543 and 1566. He compiled his results into An Annotated Census of Copernicus’ De Revolutionibus, which describes the provenances, annotations and margin notes, and condition of all surviving 16th-century copies of this major Renaissance text. “I began this census to gain new insights about Copernicus at the 500th anniversary of his birth in 1973, but the project took on a life of its own as I gradually began to realize how much we could learn about the early reception of Copernicus’ radical ideas. Radical not for us, but for those 16th-century skeptics, and that’s of course what makes it so interesting,” says Gingerich. Gingerich’s survey has led to new understanding of how scientists communicated in the late 1500s.