By these three preliminary moves:

1. the shifting of the system's centre into the sun;
2. the proof that the orbital planes do not "oscillate" in space, and
3. the abolition of uniform motion,

Kepler had cleared away a considerable amount of the rubbish that had obstructed progress since Ptolemy, and made the Copernican system so clumsy and unconvincing. In that system Mars ran on five circles; after the clean-up, a single eccentric circle must be sufficient — if the orbit was really a circle. He felt confident that victory was just around the corner ...

Arthur Koestler
"The Watershed: The Giving of the Laws"
The Sleepwalkers  (1959)
A History of Man's Changing Vision of the Universe