KIRCHER  &  THE  WORLD   SYSTEMS
Dr Robert A. Hatch - University of Florida


Athanasius Kircher (1601/2-1680) presents six world systems in his Iter extaticum coleleste of 1660 (p.37) representing geocentric, heliocentric, and geo-heliocentric variations.  The top left diagram illustrates the Systema Ptolemaicum. the model of Claudius Ptolemy (fl. 140 AD) where the earth is fixed and stable at the center of the cosmos, then (moving outward) the earth is circled by the Moon, Venus, Mercury, the Sun, Mars, Jupiter, Saturn, and finally the sphere of fixed stars. 
The second illustration (top right) is the Systema Platonicum, an alleged model of the great philosopher Plato (427-347 BC), where the earth is fixed and stable at the center, then (moving outward) the earth is circled by the Moon, the Sun, Venus, Mercury, Mars, Jupiter, Saturn, and finally the sphere of fixed stars.  It should be noted that a number of schemes have been attributed to Plato, including axial rotation of the central, spherical earth. 
The third model (middle left) is the Systema Aegyptiacum, the so-called Egyptian System.  There is much scholarly debate about the status and pedigree of this model; the sources are weak.  In the Egyptian model the central earth is fixed followed by the Moon, then Sun.  Significantly, although the Sun circles the earth annually, it is in turn circled by Venus and Mercury with their appropriate annual periods.  Outside the this 'composite orbit' then come Mars, Jupiter, Saturn, and finally the sphere of fixed stars. 
The fourth illustration (middle right) is the Systema Tychonicum, the well-known model of the great Danish naked-eye observer, Tycho Brahe (1546-1601).  As discussed elsewhere in detail, in this model , where the earth is fixed and stable at the center, then (moving outward) the earth is circled by the Moon and the Sun.  Here there is an important variation on earlier models.  Tycho suggested that all of the 'outer' planets  (not including the Moon) circled the Sun with their appropriate annual period.  Hence, the Sun circled the earth each year and, in turn, Venus, Mercury, Mars, Jupiter, and Saturn circled the Sun.  As in all of the models so far discussed, the 'outer' sphere (for all practical purposed here) was the sphere of fixed stars; it rotated on its axis daily carrying all of the heavenly bodies below along with it. 
The fifth illustration (bottom left) is the Systema Semi-Tychonicum, a geo-heliocentric variation on the model presented by Tycho Brahe.   In this model it can easily be seen that moons (or attendants) rotate around Jupiter and Saturn.  Other variants are also possible (as with Tycho's one-time assistant, Longomontanus) to have the earth rotate daily on its axis.
The sixth and last illustration (bottom right) is perhaps the most familiar to modern readers, the Systema Copernicanum, named of course after Nicholas Copernicus (1473-1543).  In the Copernican System the sun is fixed and stable near (but not precisely at) the geometric the center of a given planet's motion.  Then (moving outward) the Sun is circled by Mercury, Venus, the earth (which was quite alone in having a Moon), and then, of course, the superior planets (above earth) Mars, Jupiter, Saturn, and finally the sphere of fixed stars.  Copernicus held that the sphere of fixed stars did not account for the daily apparent motions (the first motion), rather, that was accounted for by the daily rotation of the earth.  Copernicus did, however, ascribe other motions to earth and to the sphere of fixed stars.  Will shall not discuss these motions here.  They were intended to account for precession of the equinoxes and for trepidation, an apparent back and forth motion of the celestial fault.  Details about these motions can be found in any good study of Copernicus' work.  The most accessible primary source is Copernicus' Letter Against Werner (See Three Copernican Treatises, ed. Rosen).


A less well-known illustration of the various cosmological alternatives comes from the end of the 17th century.  As in the Kircher diagram, here again we see a number of options, and again it seems telling that primacy is given to the geocentric model (top).  Also illustrated are models of the heliocentric (middle left), Cartesian (middle right), and geo-heliocentric (bottom left) schemes.  In the lower right are Cartesian vortices.

 
  
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