"The Earth together with its surrounding waters must in fact have such a shape as its shadow reveals, for it eclipses the Moon with the arc of a perfect circle."
— Nicolaus Copernicus
The Earth Together With Its Surrounding
The Earth together with its surrounding waters must in fact have such a shape as its shadow reveals, for it eclipses the Moon with the arc of a perfect circle.
About this quote
Nicolaus Copernicus made this observational argument in Book I, Chapter 2 of De revolutionibus orbium coelestium (1543) to demonstrate that the Earth is spherical. By observing that the shadow cast by the Earth during lunar eclipses is always circular regardless of direction, he showed the Earth must be a sphere — since only a sphere casts a circular shadow from every angle. This argument had been made by Aristotle and later astronomers, and Copernicus cited it as established fact before proceeding to his heliocentric argument.
Source
De revolutionibus orbium coelestium, Book I, Chapter 2, 1543
