Revistes Catalanes amb Accés Obert (RACO)

Al-Bīrūnī: The Plate of the Eclipses

Flora Vafea


This paper focuses on an extract from the treatise of al-Bīrūnī (973-1048 AD) Comprehension of the possible ways for the construction of the astrolabe, where “the plate of the eclipses” is described. This is a device that can be attached on the back side of the astrolabe. It consists of a plate, engraved on both sides, and a grid that can be attached to either side of the plate and can rotate upon it. Given the date of the lunar month, one can find the time of the moon rising and the phase of the moon, using the front side of the plate. Knowing the latitude of the moon at the opposition, one can determine whether there will be a lunar eclipse or not, using the back side of the plate, and can also estimate the magnitude, start time and duration of the eclipse. The results are approximate.

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