The picture on the left: Astrolabe, dated 1594, Brass; British Museum, London
Astrolabe is used to give a picture of the sky's view at observer's latitude and time.
It is suspended by a small hook or "eye" which hung in a vertical plane. It has moveable parts that can be set for specific dates and times, and interchangeable templates that can set latitude. A rod of ring's diameter length is pivoted at the center of the ring, carrying sights at either end. When aligned on a star or planet, an angular scale inscribed on the armillary ring gives the object's altitude.
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