Commentariolus

The Commentariolus (Little Commentary) is Nicolaus Copernicus's 40-page outline of an early version of his revolutionary heliocentric theory of the universe. After further long development of his theory, Copernicus published the mature version in 1543 in his landmark work, De revolutionibus orbium coelestium (On the Revolutions of the Heavenly Spheres).

Copernicus wrote the "Commentariolus" in Latin some time before 1514 and circulated copies to his friends and colleagues. It thus became known among Copernicus's contemporaries, though it was never printed during his lifetime. In 1533, Johann Albrecht Widmannstetter delivered a series of lectures in Rome outlining Copernicus' theory. Pope Clement VII and several Catholic cardinals heard the lectures and were interested in the theory. On 1 November 1536, Nikolaus von Schönberg, Archbishop of Capua and since the preceding year a cardinal, wrote to Copernicus from Rome and asked him for a copy of his writings "at the earliest possible moment".

Although copies of the "Commentariolus" circulated for a time after Copernicus's death, it subsequently lapsed into obscurity, and its previous existence remained known only indirectly, until a surviving manuscript copy was discovered and published in the second half of the nineteenth century.