Pseudo-Bede: De Astrolabio

This short treatise explains how to construct an astrolabe, the instrument used to model the heavens and measure the positions of the stars. It begins with the three circles drawn first, those of Capricorn, of Libra and Aries, and of Cancer, and describes how the middle circle is divided into four quarters by lines and the whole into 360 parts, with arcs of twenty-four parts marked off to find the other circles. The geometrical steps are given with reference to lettered points in a figure. Further sections deal with the arrangement of the climates and with the measurement of the rete, the pierced plate that carries the stars.

Although printed among the doubtful works of Bede, the treatise belongs to a much later period: knowledge of the astrolabe reached the Latin West from Islamic Spain from the late tenth century onward, and the text still uses an Arabic-derived technical term, alcotum. Its author and exact date are unknown. It is a witness to the early transmission of Arabic astronomical instruments into Latin learning.