made in Tabriz, Iran in 2013
An astrolabe is an elaborate inclinometer, historically used by astronomers and navigators to measure the altitude above the horizon of a celestial body, day or night. It can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, or to triangulate. It was used in classical antiquity, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes.
The astrolabe’s importance not only comes from the early development of astronomy, but is also effective for determining latitude on land or calm seas. Although it is less reliable on the heaving deck of a ship in rough seas, the mariner’s astrolabe was developed to solve that problem.
Al-Biruni quotes and criticizes medieval scientist Hamzah al-Isfahani who stated: “asturlab is an arabization of this Persian phrase” (sitara yab, meaning “taker of the stars”). In medieval Islamic sources, there is also a folk etymology of the word as “lines of lab”, where “Lab” refers to a certain son of Idris (Enoch). This etymology is mentioned by a 10th-century scientist named al-Qummi but rejected by al-Khwarizmi.
Astrolabes and clocks
Mechanical astronomical clocks were initially influenced by the astrolabe; they could be seen in many ways as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets.
Many astronomical clocks use an astrolabe-style display, such as the famous clock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmaker Dr. Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with Ulysse Nardin in 1985. Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.