Thoughts on John of Saxony's method for finding times of true syzygy

✍ Scribed by Richard L. Kremer

• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 122 KB
• Volume: 30
• Category: Article
• ISSN: 0315-0860
• DOI: 10.1016/s0315-0860(02)00025-3

✦ Synopsis

This article examines John of Saxony's iterative method for finding the times from mean to true syzygy (i.e., conjunction or opposition of the Moon and Sun). It argues that the method, composed c. 1330, contains several ambiguities, but is so robust that only one of these ambiguities affects the time correction. Furthermore, the method yields times of true syzygy that correspond, to the nearest minute, to the time when the true elongation, as computed by the planetary equations of the 1483 Alfonsine Tables, makes its closest approach to 0 • or 180 • . Hence John's method yields "exact" Alfonsine times, unlike all other known medieval methods or tables that only approximate those results. It will also be shown that John Somer (1380s) and Regiomontanus (1440-1450s) wielded John's method with considerable computational skill.