Sky & Telescope June 1981 [antikvár]

Render Not UntoTycho That Which Is Not BrahesEdward Rosen, City University of New YorkA COPY of Nicholas Copernicus' On the Revolutions of the Heavenly Spheres, previously unnoticed in the Vatican Library, was first brought to the world's attention in 1973. Copernicus' Revolutions shattered peoples' millennial misconception that their home on Earth was forever unmoved and immovable in the center of the universe. It also revealed that the loops regularly traced by a planet as it majestically courses through the heavens are illusions.As Copernicus first showed, the observed rétrogradations do not result from any planets shifting into reverse gear. It is only because we watch them from an Earth moving faster or slower than they do that they seem to us to be looping along. An extraterrestrial spectator stationed some-where in space and at rest with respect to the planetary ballet would see no loops, only a set of celestial bodies always forging ahead. This reduction of the planetary loops to a geometric effect constituted Copernicus' most convincing proof that the Earth was itself a planet in motion. That proof has withstood the test of time, having been used for centuries all over the civilized world to introduce planetary theory to beginners.Back in the 16th century, however, the Copernican Earth in motion was thought by some people to contradict the Bible. They wanted to get rid of this (allegedly) nonbiblical moving Earth. But at the same time they also wished to banish the planetary loops. There was more than one way for a semi-Copernican to abolish theThe semi-Copernican astronomer who annotated the Vatican copy of Copernicus' On the Revolutions of Ike Heavenly Spheres sketched this diagram showing the three outer planets orbiting the Earth. The Moon was depicted in a similar orbit, as was the Sun around which Mercury and Venus revolved. The photographs with this article were supplied by the author.To reproduce the apparent motions of planets in the sky, using only circular orbits and uniform velocities, ancient astronomers adopted the epicycle-def-erent system depicted here.loops while keeping the Earth stationary at the center of the universe.VATICAN'S COPERNICUSBound into the back of the recently discovered Vatican copy of Copernicus' Revolutions are some manuscript sheets, written by someone who did not disclose his name. On the back of the folio now numbered 201 he wrote in red ink in the upper left corner: "The theories that follow were derived by me from the preceding hypothesis of Copernicus in the year [15]78." Thus, on February 1st (folio 205) he drew "A Different Theory of the Three Outer Planets, derived from Copernicus, Book III, Chapter 20." His Earth, like Copernicus', was in motion on February Ist. But by February 13th he devised a "Theory of the Three Outer Planets Adjusted to a Stationary Earth."Using the traditional pattern of deferent and epicycle, he arbitrarily made his epicycle's radius equal to the radius of the Copernican Earth's orbit. This he drew as a dashed circle, to show that for him it was now merely a dimension, whereas his epicycle was an unbroken circle. On February 14-16 he constructed models for Mercury and Venus. Then, on February 17th, he assembled the separate parts in his culminating diagram, labeled "In Accordance with Copernicus' Hypotheses, the Sphere of the Revolutions, Adjusted to a Stationary Earth." The Earth is placed at the center of the universe, with the Moon revolving around it. The Sun also revolves around it. while Mercury and Venus orbit the Sun. But the three outer planets (Mars. Jupiter, and Saturn) circle the Earth.However, in an alternative planetary476 Sky and Telescope. June. 1981