The "Commentariolus" ("Little Commentary") is Nicolaus Copernicus's forty-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" 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.
Copernicus offered seven postulates:
- Celestial bodies do not all revolve around a single point
- The centre of Earth is the centre of the lunar sphere—the orbit of the moon around the Earth
- All the spheres rotate around the Sun, which is near the centre of the Universe
- The distance between the Earth and the Sun is an insignificant fraction of the distance from the Earth and Sun to the stars, so parallax is not observed in the stars
- The stars are immovable; their apparent daily motion is caused by the daily rotation of the Earth
- Earth is moved in a sphere around the Sun, causing the apparent annual migration of the Sun; the Earth has more than one motion
- Earth's orbital motion around the Sun causes the seeming reverse in direction of the motions of the planets.
- Koyré (1973, pp.18–28); Rosen (2004, pp.6–7, 57–90). Thoren (1990, p.99) gives the length of the manuscript as 40 pages.
- A reference to the "Commentariolus" is contained in a library catalogue, dated May 1st, 1514, of a 16th-century historian, Matthew of Miechow, so it must have begun circulating before that date (Koyré, 1973, p.85; Gingerich, 2004, p.32).
- Schönberg, Nicholas, Letter to Nicolaus Copernicus, translated by Edward Rosen.
- Tycho Brahe obtained a copy in 1575, and subsequently presented copies to students and colleagues as tokens of his esteem (Dreyer, 1890, p.83; Thoren, 1990, pp.98–99)
- According to Rosen (2004, pp. 6–7), a manuscript copy of the "Commentariolus" was discovered in Vienna and published in 1878. According to Koyré (1973, p. 76), a very poor copy was published in the 1854 Warsaw edition of De revolutionibus.
- Goddu, André (2010). Copernicus and the Aristotelian tradition. Leiden, Netherlands: Brill. pp. 245–6. ISBN 978-90-04-18107-6.
- Dreyer, John Louis Emil (1890). Tycho Brahe; a picture of scientific life and work in the sixteenth century. Edinburgh: Adam and Charles Black.
- Gingerich, Owen (2004). The Book Nobody Read. London: William Heinemann. ISBN 0-434-01315-3.
- Koyré, Alexandre (1973). The Astronomical Revolution: Copernicus – Kepler – Borelli. Ithaca, NY: Cornell University Press. ISBN 0-8014-0504-1.
- Rosen, Edward (translator) (2004) . Three Copernican Treatises: The Commentariolus of Copernicus; The Letter against Werner; The Narratio Prima of Rheticus (Second Edition, Revised ed.). New York, NY: Dover Publications, Inc.
- Thoren, Victor E. (1990). The Lord of Uraniborg. Cambridge: Cambridge University Press. ISBN 0-521-35158-8.
- http://www.fh-augsburg.de/%7Eharsch/Chronologia/Lspost16/Copernicus/kop_c00.html Complete Latin text online at Bibliotheca Augustana.
- http://dbanach.com/copernicus-commentarilous.htm — Edward Rosen's (2004, pp.57–65)) English translation of the first four sections.