The wisest philosophers and the ablest astronomers agreed with the age-old belief of the common people that the earth is motionless. But the competing astronomical systems based on a stationary earth had to resort to unnecessary complications. The desire to get rid of a basic complication impelled Copernicus to proclaim the earth's true cosmic status as a natural satellite of the sun. This innovation of Copernicus started the scientific revolution, which has continued from his time to ours and is still going on. The authors's investigations are freshly presented here in a concise and fascinating form.