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Astronomical use of the plane astrolabe
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The plane astrolabe may have been invented in Alexandria of Egypt as early as the second century B.C.E. It was successfully disseminated in the medieval Muslim world and, via Muslim Spain, penetrated into Europe in the tenth century.

The astrolabe parts are fitted onto a central axis. The body of the instrument is called the mater, a thick plate with a graduated limb and a ring from which it can be suspended. Inserted into the mater is the tympanum or latitude plate, which carries the projections of the observer's altazimuth coordinates with the main vertical circles and the main altitude parallels. The rete is a disk showing the Sun's annual path and the positions of selected bright stars.

With an alidade, or straight rule with sights, placed on the back of the astrolabe, the observer aims at one of those stars to measure its altitude. The rete is then rotated until the star indicator overlaps the altitude parallel corresponding to the measurement. On a twenty-four hour scale, the time of night is given by the angle between the position of the Sun on the observation day, recorded with a marker, and a fixed direction.

If, instead, the day and hour are known, one can predict the star's altitude. And also, for any given day, one can determine the time of a heavenly body's rising, culmination, and setting.

Objects
Astrolabe

Astrolabe

Inv. 1093
Thomas Gemini, English, 1550-1559

Astrolabe

Astrolabe

Inv. 1094
Gualterus Arsenius [attr.], Flemish, ca. 1570

Astrolabe

Astrolabe

Inv. 1095
Charles Whitwell, English, 1595

Astrolabe

Astrolabe

Inv. 1097
Johann Richter (Praetorius), Altdorf, 1591

Astrolabe

Astrolabe

Inv. 1100
Maker unknown, English?, late 16th cent.

Astrolabe

Astrolabe

Inv. 3361
Egnazio Danti or Giovanni Battista Giusti [attr.], Florence, 16th cent.

Astrolabe

Astrolabe

Inv. 1103
Gualterus Arsenius, Louvain, 1572

Astrolabe

Astrolabe

Inv. 1098
Gerard Mercator [attr.], Duisburg, ca. 1570

Astrolabe

Astrolabe

Inv. 1123, 1124, 1127
Charles Whitwell [attr.], English, late 16th cent.

Fragments of paper astrolabes

Fragments of paper astrolabes

Inv. 1289bis
Maker unknown, Florence?, 17th cent.

Plane astrolabe

Plane astrolabe

Inv. 660, 1092
Maker unknown, Tuscany?, 17th cent.

Plane astrolabe

Plane astrolabe

Inv. 1113
Maker unknown, Arab, 10th cent.

Plane astrolabe

Plane astrolabe

Inv. 1109
Maker unknown, Arab, 14th cent. (?)

Plane astrolabe

Plane astrolabe

Inv. 1105
Muhammad 'Ibn Abi'l Qasim 'Ibn Bakran, Arab, 1102-1103

Plane astrolabe

Plane astrolabe

Inv. 1289
Vincenzo Viviani [attr.], Italian, 1645

Plane astrolabe

Plane astrolabe

Inv. 1106
Maker unknown, German?, 16th cent.

Plane astrolabe

Plane astrolabe

Inv. 1107
Maker unknown, French?, 13th cent.

Plane astrolabe

Plane astrolabe

Inv. 1114
Christoph Schissler, Augsburg, 1560

Plane astrolabe

Plane astrolabe

Inv. 1285
Maker unknown, Italian, 1568

Plane astrolabe

Plane astrolabe

Inv. 1282
Maker unknown, German, 16th cent.

Plane astrolabe

Plane astrolabe

Inv. 1096
Hans Dorn [attr.], German, 1483

Plane astrolabe (open)

Plane astrolabe (open)

Inv. 1111
Georg Hartmann, Nuremberg, 1545