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拍品專文
The astrolabe's origin probably dates at least as far back as the ancient Greek astronomer Hipparchus (c. 190-120 BC). As with so much astronomy, through the traditions of medieval Islamic science it was reintroduced to the Latin West by the thirteenth century, where it became a key time-telling instrument. Their production in Europe reached its zenith in the late Renaissance when they were made for princely collections and came to be the iconic instrument of astronomical knowledge.
A brass plate, the rete, carries hooked pointers for named stars and acts as a rotating celestial map above a grid that shows the lines of altitude and azimuth in the night sky; the owner of the astrolabe would be able to change the plate carrying the grid depending on how far North or South they were -- the mapping of the night sky onto a flat disc is done via a stereographic projection. The reverse of the astrolabe carries a compendium of different projections, a sundial and grid for trigonometry calculations, a calendar and a shadow square that can be used to measure the heights of buildings. Around the back plate rotates an alidade with pinhole sights that are used to observe the height of the Sun or a given star (the taking of a star's position gives the ancient greek etymology astro-labos, 'star-taker').
A recent discovery in Spain, the simple throne of this astrolabe shows the influence of the Islamic tradition of astrolabists. While the engraving is very rubbed in places, beneath the alidade on the reverse it was protected form corrosion and is of late Gothic style. Using the method published by Jon Davis 'Dating as Astrolabe from its Calendar Scale' Bulletin of the Scientific Instrument Society, No. 137, 2017 a production in the second half of the 15th century can be inferred.
A brass plate, the rete, carries hooked pointers for named stars and acts as a rotating celestial map above a grid that shows the lines of altitude and azimuth in the night sky; the owner of the astrolabe would be able to change the plate carrying the grid depending on how far North or South they were -- the mapping of the night sky onto a flat disc is done via a stereographic projection. The reverse of the astrolabe carries a compendium of different projections, a sundial and grid for trigonometry calculations, a calendar and a shadow square that can be used to measure the heights of buildings. Around the back plate rotates an alidade with pinhole sights that are used to observe the height of the Sun or a given star (the taking of a star's position gives the ancient greek etymology astro-labos, 'star-taker').
A recent discovery in Spain, the simple throne of this astrolabe shows the influence of the Islamic tradition of astrolabists. While the engraving is very rubbed in places, beneath the alidade on the reverse it was protected form corrosion and is of late Gothic style. Using the method published by Jon Davis 'Dating as Astrolabe from its Calendar Scale' Bulletin of the Scientific Instrument Society, No. 137, 2017 a production in the second half of the 15th century can be inferred.