Wikipedia:Picture of the day/December 31, 2004
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An 18th century Persian Astrolabe. During the age of sail, the astrolabe was the chief instrument for navigation. It is a precursor of the modern planisphere — the back plate, or mater is engraved with coordinate lines of the celestial sphere in stereographic projection, the points of the curved spikes on the front rete plate, mark the positions of the brightest stars. Photo credit: Solipsist |