I am much occupied with the investigation of the physical causes [of motions in the Solar System]. My aim in this is to show that the celestial machine is to be likened not to a divine organism but rather to a clockwork ... insofar as nearly all the manifold movements are carried out by means of a single, quite simple magnetic force. This physical conception is to be presented through calculation and geometry.

I measured the skies, now the shadows I measure, Sky-bound was the mind, earth-bound the body rests. [Kepler's epitaph]

Since we astronomers are priests of the highest God in regard to the book of nature, it befits us to be thoughtful, not of the glory of our minds, but rather, above all else, of the glory of God.

If God himself has waited six thousand years for someone to contemplate his works, my book can wait for a hundred.

My greatest desire is that I may perceive the God whom I find everywhere in the external world, in like manner also within and inside myself.

Nature loves simplicity and unity.

I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses.