800 Years of Alfonso X – King Alfonso and the Path of the Planets

Alfonso X – the wise – was very committed to art and science (Libro de los juegos)

He learned Ptolemaic cosmology from the Moroccans. Then the sun and planets revolve around the earth and follow many intervening circular motions.

On the basis of this worldview, he had the motion of the planets pre-calculated as accurately as possible. After nearly two decades of work, in 1270 the most accurate planetary tables to that point were completed.

The accounts were directed by scholars Yehuda ibn Musa and Ishaq ibn Sayyid, whose lives not much is known. Both wrote one of the most important works in the history of astronomy, although it is named after the project’s sponsor.

Saturn with wide open rings

Alfonsine’s tables gave pre-calculated positions of the trajectory of Saturn and the other planets. (Hubble/NASA/ESA)

The “Alfonsine Tables” gained attention throughout Europe – and shaped astronomy for two centuries. But the tables were based on a false assumption: the Earth is not at the center of the solar system.

This flaw is becoming more and more apparent over time. Around the year 1500, the planets in the sky were four diameters from the full moon from the position given in the Alfonsine tables.

This made some Nicholas Copernicus think of a new view of the world – he very wisely moved the Earth to the edge and the Sun to the center of the planetary system.

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