Handbook of 809

The so-called Aachen Compilation of 809–812, also called (by Ramírez-Weaver in his 2008 dissertation) the Handbook of 809 is a Carolingian astronomical compendium, compiled by a group of astronomers who gathered at the court of Charlemagne at Aachen in the year 809.

Charged with assessing the state of current knowledge about the heavens, they drew from classical sources such as the Historia naturalis by Pliny and the Greek tradition based on the Phaenomena by Aratus of Soli.

But the aim of the Carolingian review of astronomy was to Christianize this "pagan" scientific tradition, using a strategy which attempted to keep as much material as possible of the ancient authors while taking care to alter some details which had given cause for concern in early medieval Christian doctrine.

De ordine ac positione stellarum in signis is a catalogue of 42 constellations (out of the total of 48 listed by Ptolemy).

Another early copy of the handbook survives in the Biblioteca Nacional de España in Madrid, as Ms. 3307.