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Astrolabes serve two purposes. First, they are useful as an astronomical tool, especially for finding a ship\u2019s latitude. But second, they are works of art in themselves. Besides having to be precise, many are beautiful. They are even seeing a resurgence in popularity as collectors lap up even those made by modern manufacturing processes because of their aesthetic appeal. Now, a new paper adds to their uses \u2013 a self-referential ability to mark what year they were made by the patterns of the stars they reference.<\/p>\n
<\/p>\n Emmanuel Davoust is a professional astronomer at the Observatorie Midi-Pyrenees in Toulouse, France. He\u2019s also somewhat of an amateur historian. In a paper recently released on arXiv, he analyzes the positions of stars as where they would be with reference to the pointers on an astrolabe located in the Musee des Arts precieux Paul-Dupuy<\/em>, also in Toulouse.\u00a0<\/p>\n Constructing an astrolabe is a complicated process and requires the manufacture of several parts with arcane names such as the \u201crete\u201d, which \u201crepresents a planar projection of the celestial sphere,\u201d and the \u201cmater\u201d \u2013 not referring to the animated Disney character, but the disc with graduations on the back that allow the user to determine a star\u2019s height over the horizon.<\/p>\n But perhaps most importantly, astrolabes have \u201cpointers\u201d that, when placed against the sky, would represent the position of a particular set of stars. The astrolabe Dr. Davoust studied has 34 of these, though none are named.\u00a0<\/p>\n The solution to understanding what stars are at the end of the pointers might seem simple \u2013 hold the astrolabe out at different places in the sky until all 34 pointers point at something (and at Polaris \u2013 which must be located in the center of the rete). However, despite seemingly staying stationary in the night sky, stars do move over long periods \u2013 for example, over centuries.<\/p>\n That slow, drifting movement is what Dr. Davoust used to date the astrolabe. Since the astrolabe lacked an obvious take of manufacture from the Dominican friars who made it, and none of the stars at the end of the pointers were named, it was time to bring modern technology into the effort.<\/p>\n \n
Credit \u2013 Emmanuel Davoust<\/figcaption><\/figure>\n<\/div>\n