As astronomy went through its revolutionary transformation from the time of Copernicus to Newton, the ground shifted from mathematical modeling to deep probings of the structures of the universe. We have seen already that seventeenth-century European natural philosophers had stumbled onto the mysterious forces of magnetism and electricity. Solving the problem of the orbits of the planets was not just a mathematical problem based on observational parameters for the seven planets. Sooner or later, astronomers would be released from the confines of geometry to the soaring world of philosophers of the universe such as Galileo wished to be. That meant grasping the forces of nature, both large and small.

Philosophers of the Universe

This was to be the new age of cosmology. Inevitably, it required working toward a unified science of terrestrial and celestial physics. Kepler was the first of these new philosophers of the universe to propose a new astronomy based on physical causes, something missing from Copernicus's great work. Yet, even he did not envision a unified terrestrial and celestial physics, as Newton did. He had a grand vision for the shape of astronomy based on physical causes, but just what that meant in Kepler's time, nobody could say. He laid out that vision in an insight from 1605 that was not published until the appearance of his New Astronomy of 1609:

To propose a machinelike universe animated by a single force was audacious. Galileo was a committed Copernican, and his extraordinary visual exploration of the heavens using the telescope yielded the discovery of the cratered surface of the moon, the satellites of Jupiter, and the phases of Venus, all of which supported the Copernican hypothesis as he saw it. Yet, he did not have a grander vision of celestial physics beyond the success of the Copernican system.