In the Commentariolus (Little Commentary), Nicolaus Copernicus outlined his revolutionary Copernican heliocentrism theory of the solar system, about three decades before he finally published his major six volume work De revolutionibus orbium coelestium in 1543.
Copernicus did not publish the Commentariolus, and handed it only to few friends. It is unknown who received the Commentariolus, and when. He had written the preliminary manuscript description of his early version of the theory sometime before 1515. Some scholars believe it was as late as 1533 due to the maturity of the theory. It was never printed or otherwise published during Copernicus's lifetime, and its existence was only known indirectly until copies were published in the second half of the nineteenth century.
The only other astronomical work written by Copernicus, besides the Commentariolus and De Revolutionibus, was a letter written in 1524 to one of his former fellow students at the Cracow Academy, Bernard Wapowski (The Letter against Werner). This letter, which, like the Commentariolus, circulated in manuscript but was not published during Copernicus's own lifetime, criticized De motu octauæ Sphæræ tractatus primus, a work published in 1522 by Johannes Werner, which outlined a method of trepidations to account for purported variations in the rate of precession of the equinoxes.
The Commentariolus was known among scholars. In 1533, Johann Albrecht Widmannstetter delivered in Rome a series of lectures outlining Copernicus' theory. The lectures were heard with interest by Pope Clement VII and several Catholic cardinals. On 1 November 1536, Nikolaus Cardinal von Schönberg, Archbishop of Capua, wrote a letter to Copernicus from Rome, urging him to publish.
Georg Joachim Rheticus and Tiedemann Giese then compiled an introduction to Copernicus' theory, the Narratio Prima, to be published by Franz Rhode in 1540. This was instrumental for Copernicus' approval to publish De revolutionibus.
1. ^ Koyré (1973, pp.25-28, 85-86)
2. ^ According to Koyré (1973, p.76), a copy was published in the 1854 Warsaw edition of De Revolutionibus. Rosen (2004, pp.9,11), however, while mentioning that copies of The Letter against Werner and Narratio prima had appeared in that edition of De Revolutionibus, does not do so for the Commentariolus. The earliest publication date given by Rosen (2004, pp.6-7) for the Commentariolus is that of a copy found in Vienna and published in 1878.
3. ^ Rosen (2004, pp.7-9)
* 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, New York, NY: Dover Publications, Inc.
* 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.