Some sources (modern sources, and Kepler himself) claim that in his Geo-Heliocentric (Tychonic) model, Tycho Brahe saw that the orbs of the Sun and Mars intersect, and this was one of the reasons which led him to reject the Solid Orbs:
When Tycho first devised his system, he was still thinking of celestial bodies being imbedded in solid orbs. However he found that in his geo-heliocentric system, the orb of Mars intersected the orb of the sun. This led Tycho to [reject the solid orbs]. (The Oxford Handbook of Early Modern European History, 1350-1750. p.70 ).
I have two questions (I would appreciate even reply to one of those questions):
Why this could not be shown earlier using the traditional Ptolemy form. Was that Geo-Heliocentric model that was necessary, or merely new numbers(?) that Tycho plugged in?. For on first sight I can't see why; since, if there is a point in the orb of Mars that is closer to the Earth, than some other point in the orb of the Sun, why couldn't this be seen also in Ptolemy system where the epicycle of Mars must also intersect the eccentric of the Sun (If we would plug the same numbers to make the models equivalent with respect to the vision from Earth).
In Kepler's Astronomia Nova he thus writes in chapter 6 (Translation William H. Donahue):
Nevertheless, in the theory of Mars, the planet's eccentric is so small in proportion to the Sun's eccentric that Mars's eccentric and the point O and F are nearer to the Earth C than is the sun S, which was one of the reasons why Brahe denied the solidity of the orbs
I'm not quite sure I understand what Kepler means by "planet's eccentric is so small in proportion to the Sun's eccentric" because how could it be that the eccentric of Mars be smaller than the Sun's?