On a Sixteenth-Century Empirical Disproof of Ptolemaic Geocentrism
The significance of the book Alae seu Scalae Mathematicae (Mathematical Wings or Ladders) published by Thomas Digges in 1573, has long been under-estimated. The book reports on an empirical disproof of Aristotelian–Ptolemaic geocentrism based on diurnal parallaxes measured and derived by a “new and unheard-of method.” Digges’ mathematical theorems on data measurement and reduction comprise the bulk of Alae seu and replace the method of Regiomontanus which needed accurate time intervals between observations that existing clocks could not supply. Evidence suggests that Digges obtained planetary parallaxes of sufficient accuracy to assert that planets do not circle the Earth at a constant distance but have some other center or centers. His well-known cartoon of an infinite universe of stars containing a planetary system centered on the Sun appears to be an inductive adoption of the Copernican system justified by his planetary parallax determinations. He claims that this was accomplished by use of “a new kind of instrument” which he promised to discuss in a book entitled “Commentaries upon the Revolutions of Copernicus,” provided his work met with approval, but the book never appeared. In 1579, Digges explains the reasons, among which are the quality of his home life, his isolation, and law suits. This year is a good time to celebrate the 450th anniversary of the publication of Alae Seu.
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| Work Title | On a Sixteenth-Century Empirical Disproof of Ptolemaic Geocentrism |
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| Subtitle | American Astronomical Society Meeting #241, id. 158.01. |
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| License | CC BY-NC-SA 4.0 (Attribution-NonCommercial-ShareAlike) |
| Work Type | Poster |
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| Publication Date | January 31, 2023 |
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| Deposited | March 23, 2025 |