I certainly know that I owe it [the Copernican theory] this duty, that as I have attested it as true in my deepest soul, and as I contemplate its beauty with incredible and ravishing delight, I should also publicly defend it to my readers with all the force at my command.

Vol. VI, p. 116, Vol. VIII, p. 266ff. - Joannis Kepleri Astronomi Opera Omnia, ed. Christian Frisch (1858)