THE SIXTEENTH-CENTURY EMPIRICAL DISPROOF OF PTOLEMAIC GEOCENTRISM

: In 1573, Thomas Digges published a book entitled Alae seu Scalae Mathematicae and in 2023 we celebrate the 450th anniversary of its publication. The book was prompted by the apparition of the New Star of 1572, which Digges shows does not change position in the sky. He supplies its distances from some nearby stars in Cassiopeia, but the remainder of the book has long been under-valued. It presents a “new and unheard-of method” of ascertaining diurnal parallaxes of planets, yet Digges applies the theoretical developments only in illustrative examples. However, three years later in 1576 in an essay “A Perfit Description of the Caelestiall Orbes,” Digges makes the astounding claim that he has measured parallaxes of planets with sufficient accuracy to show that they do not circle the Earth at a constant distance but have some other center or centers. This paper examines Digges’ claim of an empirical disproof of geocentrism in the sixteenth century and its support for heliocentrism.