Three-section orbs

[Linda]

From the perspective of Earth, the cosmic boundary represents the limits of knowledge. Yet the VMs has a circle and curved spokes beyond the cosmic boundary.

If something is supposed to be moving, what is it that moves? If the Earth and the whole cosmos rotate like a disk, then from the perspective of Earth, the apparent net motion is zero. Otherwise, in the wheel and hub model, the Earth is stationary.

That has always bothered me too, about the two being connected to the same ring. 

But perhaps we can forgive that, pending knowing what they meant to convey. 

Perhaps there are dual channels in that ring, or the connections to the firmament or earth are more complex than initially noticeable. The question then would be do both move or are they trying to say the Earth movements cause more than one kind of movement? The earth turns on its axis, so we have night and day and the stars appear to progress through the night. The earth moves around the sun, so that what is seen to turn changes over time on a yearly basis (but they didn't know that yet, so would be perceived as the firmament also moves). 

The earth wobbles, so there is precession of the equinoxes over thousands of years. They may have known that, especially since most of what we know of Hipparchus is from Ptolemy, whose works were being translated in the early 1400s. The sun also moves through the galaxy, so there are changes from that as well over time, they probably didn't know that.. And, things do change in the firmament, stars go nova, become nebulae which change over time, some things just go dark, etc. And everything is moving away from us at accelerated speeds and things go missing forever from our ability to ever see them again due to expansion of space, which itself isnot constant and depends on viewpoint. (I am sure those parts are not represented).

So, they might have just erred on the mechanics of drawing a simple armillary sphere, and meant to say both move, as Rene suggested.