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John of Murs computing eclipses!

Escorial

The little table at the bottom margin of the page records the fundamental element of a Solar eclipse. According to the information here this solar eclipse took place on July 7, 1339, had a maximum intensity at 2h 11min and 20 sec after noon for a total duration of 2h13min and 22 sec. The precision of these values, far beyond the range of naked eye observations, clearly indicate that they are coming from a computation.

These kinds of computation records, of eclipses or any other astronomical phenomena, are rare and precious. However, Alfonsine astronomers progressively developed a trend of noting down computations in their manuscripts, or even systematically as a type of commentary to astronomical treatises. This proved to be a long lasting initiative as well into the modern period this habit was maintained by European astronomers.

In this manuscript we find many such computation records. It can be considered as one of the first witnesses of such a practice. Moreover we know who is the author of these computations. It is John of Murs, one of the most important Parisian astronomers of the early 14th century responsible for the recasting in Latin of the Alfonsine tables.