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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Commentariolus | 1/3 | https://en.wikipedia.org/wiki/Commentariolus | reference | science, encyclopedia | 2026-05-05T08:32:52.246082+00:00 | kb-cron |
The Commentariolus (Little Commentary) is Nicolaus Copernicus's brief 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 by 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.
== Summary == The Commentariolus is subdivided into eight sections (or chapters), of which all but the first bear brief descriptive titles. After a brief introduction, the first section states seven postulates from which Copernicus proposes to show that the apparent motion of the planets can be explained systematically.
=== The seven postulates === Celestial bodies do not all revolve around a single point. The centre of the 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 the Sun to the stars. The stars are immovable; their apparent daily motion is caused by the daily rotation of the Earth. The Earth is moved in a sphere around the Sun, causing the apparent annual migration of the Sun; the Earth has more than one motion. The Earth’s orbital motion around the Sun causes the seeming reverse in direction of the motions of the planets. The remaining seven sections are titled, in order, De ordine orbium ("The order of the spheres"), De motibus qui circa solem apparent ("The apparent motions of the Sun"), Quod aequalitas motum non ad aequinoctia sed ad stellas fixas referatur ("Equal motion should be measured not by the equinoxes but by the fixed stars"), De Luna ("The Moon"), De tribus superioribus: Saturno, Jove et Marte ("The outer planets: Saturn, Jupiter and Mars"), De Venere ("Venus") and De Mercurio ("Mercury").
=== The order of the spheres === In this section, the heavenly spheres are given in order from outermost to innermost. The outermost sphere is that of the fixed stars, which remains perfectly stationary. Then follow those of Saturn, Jupiter, Mars, Earth, Venus and Mercury, which each revolve about the Sun from west to east with successively shorter periods of revolution, Saturn's being between 29 and 30 years, Jupiter's between 11 and 12, Mars's between 2 and 3, Earth's exactly one, Venus's between 8 and 9 months, and Mercury's between 2 and 3 months. The Moon's sphere, however, revolves around the Earth in a period of one month, and moves with it around the Sun like an epicycle.
=== The apparent motion of the Sun === This section explains how the apparent motion of the Sun could arise from three separate motions of the Earth. The first motion is a uniform revolution, with a period of one year, from west to east along a circular orbit whose centre is offset from the Sun by 1/25 of the orbit's radius. The second motion is the daily rotation about an axis which passes through the Earth's centre and is inclined at an angle of about 231⁄2° to the perpendicular to the plane of its orbit. The third motion is a precession of the Earth's axis of rotation about an axis perpendicular to the plane of its orbit. Copernicus specified the rate of this precession with respect to the radial line from the Earth to the centre of its orbit as being slightly less than a year, with an implied direction as being from west to east. With respect to the fixed stars, this precession is very slow, and in the opposite direction—from east to west—and explains the phenomenon of the precession of the equinoxes.
=== Equal motion should be measured not by the equinoxes but by the fixed stars === Here Copernicus asserts that the motion of the equinoxes and celestial poles has not been uniform, and argues that consequently they should not be used to define the reference frame with respect to which the motions of the planets are measured, and that the periods of the various planetary motions are more accurately determinable if those motions are measured with respect to the fixed stars. He maintains that he had found the length of the sidereal year to have always been 365 days 6 hours and 10 minutes.
=== The Moon ===