Astrolabe in use from Elvcidatio fabricae vsvsque.
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Image ID: SIL-SIL33-139-01
Original Caption: Astrolabe in use.
As you can imagine, it can be hard to keep track of all the stars in the night sky. More than 2,000 years ago, the Greeks found a way to help tackle this problem. The device called an "astrolabe" allowed them to measure the altitude of a star, or the height of a star in the sky. This early 16th Century print comes from a work by German mathematician, Johann Stoeffler, in which he explains how to construct and use an astrolabe. The astrolabe was rediscovered and further developed by Muslim scholars in the 8th and 9th centuries. In the Muslim religion, it's custom to pray at certain times throughout the day while facing in a specific direction. By using an astrolabe, people were better able to calculate time and direction. This was especially helpful since watches had not yet been invented, and compasses were uncommon.