Geometric Instruments for the Orientation and Measurement: The Astrolabes

Abstract

The astrolabe, stereographic projection of the celestial sphere on the plane of the equator, simulates the apparent rotation of this sphere around the Earth, with respect to a certain latitude, and allows to establish the relative position of the stars at a given moment. To understand its meaning and use it is necessary to recall out the main elements of astronomical geography. From the III century BC onwards, various types of astrolabe were built. Among the tools used in the course of the centuries for orientation and measurement, it is the one that perfectly performed both functions, providing measurements related to different fields of investigation: astronomy, chronometry, orientation, measurements (length-height-depth), astrology.