The astrolabe is an ancient astronomical device used  for solving problems relating to time and the position of the Sun and stars. Several types of astrolabes were made. The most common was the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator. Typical astrolabes were made of brass and about 6 inches (15 cm) in diameter. 

     Astrolabes show how the sky looks at a specific place and time. It is done by drawing the sky on the face of the astrolabe and marking it so positions in the sky are easy to find. Once you set the movable components of an astrolabe to a specific date and time, the entire sky is represented on the face of the instrument. Astrolabes were typically used time pieces during the day or night, finding the time of sunrise or sunset, and as a reference of celestial positions. Astrolabes were also one of the basic astronomy education tools in the late Middle Ages. 

     The principles of the astrolabe projection were known before 150 B.C., and true astrolabes were made before A.D. 400. The astrolabe was highly developed in the Islamic world by 800 and introduced to Europe in the early 12th century. It was the most popular astronomical instrument until about 1650, when it was replaced by more specialized and accurate instruments.

     Following are photos of an astrolabe made by Jean Fusoris in the early 1400's. At least 13 Fusoris astrolabes still exist today.

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