Copernican Heliocentrism - Acceptance of Copernican Heliocentrism

Acceptance of Copernican Heliocentrism

From publication until about 1700, few astronomers were convinced by the Copernican system, though the book was relatively widely circulated (around 500 copies of the first and second editions have survived, which is a large number by the scientific standards of the time). Few of Copernicus' contemporaries were ready to concede that the Earth actually moved, although Erasmus Reinhold used Copernicus' parameters to produce the Prutenic Tables. However, these tables translated Copernicus' mathematical methods back into a geocentric system, rejecting heliocentric cosmology on physical and theological grounds. The Prutenic tables came to be preferred by Prussian and German astronomers. The degree of improved accuracy of these tables remains an open question, but their usage of Copernican ideas led to more serious consideration of a heliocentric model. However, even forty-five years after the publication of De Revolutionibus, the astronomer Tycho Brahe went so far as to construct a cosmology precisely equivalent to that of Copernicus, but with the Earth held fixed in the center of the celestial sphere instead of the Sun. It was another generation before a community of practicing astronomers appeared who accepted heliocentric cosmology.

From a modern point of view, the Copernican model has a number of advantages. It accurately predicts the relative distances of the planets from the Sun, although this meant abandoning the cherished Aristotelian idea that there is no empty space between the planetary spheres. Copernicus also gave a clear account of the cause of the seasons: that the Earth's axis is not perpendicular to the plane of its orbit. In addition, Copernicus's theory provided a strikingly simple explanation for the apparent retrograde motions of the planets—namely as parallactic displacements resulting from the Earth's motion around the Sun—an important consideration in Johannes Kepler's conviction that the theory was substantially correct.

However, for his contemporaries, the ideas presented by Copernicus were not markedly easier to use than the geocentric theory and did not produce more accurate predictions of planetary positions. Copernicus was aware of this and could not present any observational "proof", relying instead on arguments about what would be a more complete and elegant system. The Copernican model appeared to be contrary to common sense and to contradict the Bible. Tycho Brahe's arguments against Copernicus are illustrative of the physical, theological, and even astronomical grounds on which heliocentric cosmology was rejected. Tycho, arguably the most accomplished astronomer of his time, appreciated the elegance of the Copernican system, but objected to the idea of a moving Earth on the basis of physics, astronomy, and religion. The Aristotelian physics of the time (modern Newtonian physics was still a century away) offered no physical explanation for the motion of a massive body like Earth, but could easily explain the motion of heavenly bodies by postulating that they were made of a different sort substance called aether that moved naturally. So Tycho said that the Copernican system “... expertly and completely circumvents all that is superfluous or discordant in the system of Ptolemy. On no point does it offend the principle of mathematics. Yet it ascribes to the Earth, that hulking, lazy body, unfit for motion, a motion as quick as that of the aethereal torches, and a triple motion at that.” Likewise, Tycho took issue with the vast distances to the stars that Copernicus had assumed in order to explain why the Earth's motion produced no visible changes in the appearance of the fixed stars (known as annual stellar parallax). Tycho had measured the apparent sizes of stars (now known to be illusory – see stellar magnitude), and used geometry to calculate that in order to both have those apparent sizes and be as far away as heliocentrism required, stars would have to be huge (the size of Earth's orbit or larger, and thus much larger than the sun). Regarding this Tycho wrote, “Deduce these things geometrically if you like, and you will see how many absurdities (not to mention others) accompany this assumption by inference.” He said his Tychonic system, which incorporated Copernican features into a geocentric system, “offended neither the principles of physics nor Holy Scripture”. Thus many astronomers accepted some aspects of Copernicus's theory at the expense of others. His model did have a large influence on later scientists such as Galileo and Johannes Kepler, who adopted, championed and (especially in Kepler's case) sought to improve it. However, in the years following publication of de Revolutionibus, for leading astronomers such as Erasmus Reinhold, the key attraction of Copernicus's ideas was that they reinstated the idea of uniform circular motion for the planets.

During the 17th century, several further discoveries eventually led to the complete acceptance of heliocentrism:

• Using the newly-invented telescope, Galileo discovered the four large moons of Jupiter (evidence that the solar system contained bodies that did not orbit Earth), the phases of Venus (the first observational evidence for Copernicus' theory) and the rotation of the Sun about a fixed axis as indicated by the apparent annual variation in the motion of sunspots;
• With a telescope, Giovanni Zupi saw the phases of Mercury in 1639;
• Kepler introduced the idea that the orbits of the planets were elliptical rather than circular.
• Isaac Newton proposed universal gravity and the inverse-square law of gravitational attraction to explain Kepler's elliptical planetary orbits.

In 1725, James Bradley discovered stellar aberration, an apparent annual motion of stars around small ellipses, and attributed it to the finite speed of light and the motion of Earth in its orbit around the Sun.

In 1838, Friedrich Bessel made the first successful measurements of annual parallax for the star 61 Cygni using a heliometer.

In the 20th century, orbits are explained by general relativity, which can be formulated using any desired coordinate system, and it is no longer necessary to consider the Sun the center of anything.