# "Table of Astronomy's" depiction of the solar system models

This is going to be a follow up question to my question about the "Table of Astronomy" from yesterday, What is this “Table of astronomy” about?.

I wanted to take a close look at the three depiction of the solar system models (left to right):

Fig. 43. Ptolemaic System; Fig. 45: Tychonic System; and Fig. 44: Copernican System; They are is this order in the original resource

I cant figure out what some of the symbols and circles are supposed to mean. I have marked everything im unsure about partially or completly in red.

(From left to right again)

Ptolemaic System:

The ptolemaic system is a geocentric system, meaning it has the Earth as its center. I have identified most of the symbols that mark the orbits, although I'm missing two. Furthermore, the 5 outer most orbits(?) are what I'm unsure about. As far as I understand it, Claudius Ptolemy believed not only that the Earth was the center of the universe (making this a model of the universe and not the solar system) but also, that the stars were laying on the inside of the universesphere. Therefore I can imagine that the innermost ring is just to close of the sphere. But there are still 4 rings left.

In addition to the rings, I cant identify the third (anchorlike) and the fifth symbol.

Tychonic System:

Here again I'm unsure about the two outer rings, and the third, not dotted, orbit around the Sun. The two innermost orbits are Venus and ?

If the (red)dotted orbit is supposed to be the Earth's orbit around the Sun, then why does the earth have two orbits?

Also, what are the two stars under the Moon?

Copernican System:

This one is rather straight forward. I'd like to know which of Saturn's moon's orbits this illustration depicts and if my guesses on Jupiters moons are correct.

And at last, what are the 4 marks, A, B, C and D for?

I hope you can help me! Thanks

# Ptolemaic system

### Planets

In Ptolemy's system, the two missing symbols are Venus (♀) and Mars (♂), respectively. The arc in the bottom of the Venus symbol actually belongs to Mercury below (☿).

### Stars

The two following spheres contain the stars, which were believed to be eternally fixed. The two next are, I believe, also containing stars, namely the zodiac constellations. The two last ones are the final boundary before the outside, which is the realm of God. The spheres are more discernible is this version (Petrus Apianus 1539):

# Tychonic system

### Planets and stars

In the Tychonic system, the two outermost rings again contain the fixed stars. The planets do not move between the spheres, but are fixed on the spheres, so the next sphere you ask about ("the third, not dotted, orbit") belongs to Mars (♂). The innermost one is Mercury, although its symbol (☿) isn't drawn in this version.

### Earth's and Sun's orbits

The dotted orbit isn't Earth. In the Tychonic system, Earth is in the center, and the Sun and the Moon orbit Earth, but other planets orbit the Sun. This orbit isn't drawn in many other versions; I think it's the orbit that Earth takes around the Sun, if you considered the Sun in the center (which Tycho didn't). Although it's not exactly the same size as the Sun's sphere.

### The Moon

The two stars underneath the Moon don't have anything to do with the Moon, I think, but belong to the spheres of Saturn and Jupiter. The reason I think this is that you see the same in some other versions, like this one from Tycho's De mvndi ætherei recentioribvs phænomenis (here taken from Graney (2010):

# Copernican system

### Saturn

Saturn's moons had not been discovered when Copernicus published his model in 1543. The drawing in your source is from 1728, at which time five moons had been discovered (Titan in 1655 by Christiaan Huygens; Tethys, Dione, Rhea and Iapetus between 1671 and 1684 by Giovanni Domenico Cassini). So since there are four rings, my guess is that they don't represent moons, but rather the rings, with the two midmost circles representing the Cassini Division, discovered in 1675.

### Jupiter

Your listing of the moons of Jupiter is probably correct, since that's how they're ordered according to their distance from Jupiter.

### Letters

I don't know about the letters A, B, C, and D, but my guess is that they mark the direction in which the planets revolve around the Sun, which is correct if viewed from above the ecliptic plane, i.e. the plane with respect to which Earth has an axial tilt of some 23º.

A bit more on the Ptolemaic system.

The five outer circles, from the inside out:

• Sphere of Saturn. The spheres are labeled on the inside, so this one corresponds to the Saturn symbol.
• Sphere of fixed stars. This is lableled by the star symbols, it's the sphere where all the stars are attached.

From here on out, the number and function of the remaining spheres varied a bit, but here's one version:

• Crystalline sphere. This was introduced long after Ptolemy, based on the creation story in the Bible: "And God made the firmament, and divided the waters wich were under the firmament from the waters which were above the firmament". This 'firmament that divided the waters' is the crystalline sphere.
• Primum Mobile, "first moved". This sphere rotated all the inner spheres along with it, to account for the apparent daily rotation of the sky which affects everything from the Moon to the "fixed" stars. By factoring out the common motion into a separate sphere, they got simpler models for the motion of individual inner spheres.
• Empyrean. The outermost sphere was essentially outside our universe. In ancient Greek cosmology it was the home of the elements of fire or aether, in Christian text it was where God lived.