People/Nicolaus Copernicus: Difference between revisions
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"Yet the widespread [planetary theories], advanced by Ptolemy and most other [astronomers], although consistent with the numerical [data], seemed likewise to present no small difficulty. For these theories were not adequate unless they also conceived certain equalizing circles, which made the planet appear to move at all times with uniform velocity neither on its deferent sphere nor about its own [epicycle's] center…Therefore, having become aware of these [defects], I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent irregularity would be derived while everything in itself would move uniformly, as is required by the rule of perfect motion"
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===Copernicus vs Brahe===
Brahe said that the Copernican system “expertly and completely circumvents all that is superfluous or discordant in the system of Ptolemy.... Yet it ascribes to the earth, that hulking, lazy body, unfit for motion, a motion as quick as that
of the aethereal torches.”
Another thing that bothered Brahe were the stars in the Copernican system. Ptolemy
said the sphere of the stars is “immeasurably large” because we can detect no diurnal parallax in them—no noticeable alterations in their positions or appearances caused by the changing angles and distances between an Earth-bound observer and those stars as they pass from the horizon, to overhead, to the horizon.
Copernicus knew, however, that we could not even detect annual parallax—changes
in the relative positions of stars caused by the movement of Earth in its orbit. If Earth really was revolving around the sun, the absence of annual parallax would imply that the diameter of its orbit (Copernicus called it the orbis magnus) was itself as nothing, “as a point,” compared with stellar distances. The size of the universe then became a whole new—and almost impossible to believe—kind of “immeasurably large.”
Moreover, as Brahe well knew, the Copernican proposal had big implications not only for the size of the universe but also for the size of individual stars. When we look up at the night sky, individual stars appear to have fixed widths, which both Ptolemy and Brahe measured. We now know that the distant stars are effectively point sources of light, and these apparent widths are an artifact of the passage of light waves through a circular aperture such as a telescope or an iris.
Yet at the time, astronomers knew nothing of the wave nature of light. Brahe used
simple geometry to calculate that if the stars were to lie at Copernican distances, then they would have to have a width comparable to that of the orbis magnus. Even the smallest star would utterly dwarf the sun, just as a grapefruit dwarfs the period at the end of this sentence. That, too, was hugely hard to believe—Brahe said such titanic stars were absurd. As historian Albert Van Helden puts it, Brahe’s “logic was impeccable; his measurements above
reproach.
A Copernican simply had to accept the results of this argument.”Rather than give up their theory in the face of seemingly incontrovertible physical evidence, Copernicans were forced to appeal to divine omnipotence. “These things that vulgar sorts see as absurd at first glance are not easily charged with absurdity, for in fact divine Sapience and Majesty are far greater than they understand,”
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Rather than give up their theory in the face of seemingly incontrovertible evidence, Copernicans were forced to appeal to divine omnipotence.
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When Galileo began to view the heavens with his telescope, he made a number of
findings that directly contradicted Ptolemy’s ancient cosmology. He saw that Jupiter had moons, proving that the universe could harbor more than one center of motion. He also observed the phases of Venus, showing that it circled the sun. These findings were not, however, understood as proof that Earth revolves around the sun because they were fully compatible with the Tychonic system.
===AP "Heretic to Hero" Story===
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The massive bulk of the earth does indeed shrink to insignificance in comparison with the size of the heavens.
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===Further Reading===
* [[:File:R2The case against Copernicus.pdf|PDF: The case against Copernicus]]
===References===
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