Before women could vote, Harvard Observatory was employing them to interpret astronomical observations. This book tells the stories of a Cambridge student, a young deaf woman, a pregnant Scottish housemaid and several others who between them helped to unravel the principles governing the universe.

In 1510, Copernicus had begun to formulate the theory that placed the Sun rather than the Earth at the centre of our universe. The theory was potentially heretical and not until 1539, when a young German mathematician named Rheticus sought him out, was Copernicus persuaded to publish On the Revolutions of the Celestial Spheres. Dava Sobel tells the story of the great astronomer, and where the evidence runs out, she imagines the meeting between Rheticus and the older scientist.