Ultimate Mange

I think Koestler finds Kepler to be this sort of stereotypical overzealous and defensive hurt mangy dog like person, but still lovable in a pathetic sort of way nonetheless. From childhood to growing up, Koestler never really writes of Kepler in an unfavourable light exactly. He might point out his shortcomings but ultimately Koestler writes of Kepler redeeming himself in some way.

Copernicus on the other hand seemed to just be this nervous old wishy washy wet rag who never overcame his past and upbringing in the way that Kepler did. Probably I would think Koestler was pretty frustrated with Copernicus whereas you see this zeal written about Kepler that has to indicate some sort of fondness.