February is the 551st birthday for Polish mathematician & astronomer Nicolaus Copernicus (the Latin version of Mikolaj Kopernik) [1473-1543]. He is one of the few astronomers whose work was so historic that his name is widely known, even outside the astronomical community.

It was Copernicus who first championed the modern heliocentric model for the solar system. He was certainly not the first person to have the idea that the Earth moves in orbit around the Sun. That idea dates all the way back to ancient Greece, a few hundred years BCE. However, he was the first to base his idea on detailed mathematical analysis of the motions of the planets.

Copernicus first put forward his theory in a small, anonymous pamphlet, the "Little Commentary" in 1514. But his major book, on which he labored for many years, was "De revolutionibus orbium coelestium" ("On the Revolutions of the Heavenly Spheres"), published just before his death in 1543.

Although it is commonly believed that Copernicus published his book only after his death for fear of religious opposition, this is certainly not the case. Rather, he delayed publication because of the slow progress in dealing with mathematical complications involving the motions of the planets in circular orbits. After finally being convinced by friends to publish, he received a printed copy on his deathbed.

In his intended, but unpublished preface, Copernicus said: "Perhaps there will be babblers who, although completely ignorant of mathematics, nevertheless take it upon themselves to pass judgement on mathematical questions and, badly distorting some passages of Scripture to their purpose, will dare find fault with my undertaking and censure it. I disregard them even to the extent as despising their criticism as unfounded".

He would certainly not have intended to say that if he really was worried about religious consequences of publishing the book, although not actually putting that in print was a wise move. In fact, the preface in the published version was written by a friend of Copernicus, the Lutheran preacher Andreas Osiander [1498-1552]. In that preface, Osiander carefully stated that the heliocentric model was intended only as a tool for calculation, and should not be taken literally, as if the sun were really at the center of the solar system. This made the publication safe, and avoided any serious religious criticism.

In the book, Copernicus maintained his loyalty to circular orbits, and so he had to retain the epicycles & deferents that were typical of the Ptolemaic, geocentric system, although the system of Copernicus was much less complicated.

Johannes Kepler [1571-1630], using data gathered by Tycho Brahe [1546-1601], modified the Copernican system by proving the orbits were elliptical rather than circular. This simplified the complications that had vexed Copernicus, eliminating the epicycles & deferents altogether. But there was much reluctance to accept non-circular orbits.

Galileo Galilei [1564-1642] was the first to engage in a consistent and long term program of telescopic astronomy, and he was both a forceful champion of the Copernican system, and a skilled mathematician. But he would not abandon circular orbits, even in the face of Kepler's work. Circles are "perfect" curves, while ellipses are not, and God would never put the planets in imperfect orbits, so it took much time for Kepler's obvious success to be accepted.

Galileo himself got into trouble with the church, partly because he did insist that heliocentric orbits were physically real, and not just a calculational device. But his real faux-pas was advancing his own theological implications of heliocentrism.

I have a 2002 edition of the Charles Glen Wallis translation of "On the Revolutions of the Heavenly Spheres" into English (1939), with forward by Stephen Hawking, from his "On the Shoulders of Giants" collection (Running Press, Philadelphia). The 382-page book shows off quite a bit of spherical geometry, is quite mathematically advanced for its time, and typically inscrutable to modern readers, due to its arcane geometric formalisms.

The image of Copernicus is known as the “Toruń portrait”, because it is on display at the Regional Museum of Toruń in Poland. It is dated 1580, but the artist is unknown. It is the earliest depiction of Copernicus that I am aware of.

The other image shows the diagram of the heliocentric solar system, from the 1st printed edition of "De revolutionibus orbium coelestium" (1543). The 2nd image shows a manuscript diagram, from chapter 10 of "De revolutionibus orbium coelestium”, which shows the order of the heavenly spheres (we would say orbits today), annotated with the periods. The diagram is obviously simplified, even by the standards of Copernicus, leaving out the epicycles & deferents that were still required by the circular orbits of Copernicus.

https://plato.stanford.edu/entries/copernicus/ (Copernicus - Stanford Encyclopedia of Philosophy)

https://en.wikipedia.org/wiki/Nicolaus_Copernicus (Copernicus - Wikipedia)

https://www.worldhistory.org/Nicolaus_Copernicus/ (Copernicus - World History Encyclopedia)

https://mathshistory.st-andrews.ac.uk/Biograp.../Copernicus/ (Copernicus - Mathematical biography, University of St. Andrews, Scotland)

https://www.genealogy.math.ndsu.nodak.edu/id.php?id=126177 (Copernicus - Mathematical Genealogy Project)

https://www.nmspacemuseum.org/inductee/nicolaus-copernicus/ (Copernicus - International Space Hall of Fame, New Mexico Museum of Space History)

https://www.newworldencyclopedia.org/.../Nicolaus_Copernicus (Copernicus - New World Encyclopedia)

https://www.britannica.com/.../Copernicuss-astronomical-work (Copernicus’s Astronomical Work - Encyclopedia Britannica)

https://www.scientificamerican.com/.../the-case-against.../ (”The Case Against Copernicus” - Dennis Danielson & Christopher Graney, Scientific American, 1 January 2014)

https://en.wikipedia.org/.../De_revolutionibus_orbium... (De revolutionibus orbium coelestium - Wikipedia)

https://earthobservatory.nasa.gov/features/OrbitsHistory (History of heliocentrism - NASA Earth Observatory)

https://en.wikipedia.org/wiki/Copernican_heliocentrism (Copernican heliocentrism - Wikipedia)

https://en.wikipedia.org/wiki/Copernican_Revolution (Copernican revolution - Wikipedia)

https://commons.wikimedia.org/.../File:Nikolaus... (Portrait source - Wikimedia)

https://commons.wikimedia.org/.../File:De_Revolutionibus... (Manuscript source - Wikimedia)

Originally posted by Tim Thompson, NASA JPL Senior Astronomer (Retired)

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