I used to measure the skies, now I measure the shadows of Earth. Although my mind was sky-bound, the shadow of my body lies here. [Epitaph he composed for himself a few months before he died]
The diversity of the phenomena of nature is so great, and the treasures hidden in the heavens so rich, precisely in order that the human mind shall never be lacking in fresh nourishment.
Truth is the daughter of time, and I feel no shame in being her midwife.
The squares of the periodic times are to each other as the cubes of the mean distances.
I demonstrate by means of philosophy that the earth is round, and is inhabited on all sides; that it is insignificantly small, and is borne through the stars.
I much prefer the sharpest criticism of a single intelligent man to the thoughtless approval of the masses.