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He astrolabe It is an ancient astronomical instrument probably conceived by the Greeks and used by the Arabs, the Persians and the Europeans, as an aid in navigation until the 18th century, at which time it is replaced by the most precise sextant.
It is composed of a metal disk that has a circumference graduated from 0O to 360O engraved on the edge; in a more inner band, a circle divided into 24 hours a day; in the central part, a projection of the celestial sphere in a plane parallel to the equator.
A second disk, called a network, superimposed on the first, serves as a map of the brightest stars, since it has several indexes, each of which indicates the position of a star and the corresponding name. Still superimposed on the net is a lancet, called a ruler, whose limb is superimposed on the graduated scales.
On the back of the instrument there is a scale to measure angles in degrees and a movable arm for signaling. Holding the astrolabe by the ring, suspended vertically, and properly manipulating the various parts, the height of the stars on the horizon and the time of the observation site can be measured.
The oldest specimens of astrolabs preserved in the various museums, date back to the year 1000 and are made in Arabic.
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