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observations 877-918 CE, catalog based on 880 CEReputable source · 2 sourcesWell documented

Al-Battani Refines Ptolemy's Astronomy With a New Star Catalog

Working from Syria, an astronomer corrects the length of the year and switches Greek geometry for trigonometry

On the timeline · around observations 877-918 CE, catalog based on 880 CE · Medieval and Islamic AstronomyMedieval and Islamic AstronomyAl-Battani Refines Ptolemy's Astronomy With a New Star Catalog600 CE700 CE800 CE900 CE100011001200

Quick facts

Active observation period
877-918 CE
Star catalog
489 stars, based on 880 CE
Solar year value
365 days, 5 hours, 46 minutes, 24 seconds
Method shift
Trigonometric methods in place of pure geometric construction

What happened

Al-Battani, born near Harran and active between 877 and 918 CE, made highly precise astronomical observations at Antioch and ar-Raqqah in Syria, producing a star catalog based on the year 880 CE that recorded 489 stars. He refined the existing values for the length of the year, which he gave as 365 days, 5 hours, 46 minutes, and 24 seconds, and for the length of the seasons, and he calculated the annual precession of the equinoxes at 54.5 arc-seconds per year while obtaining a value of 23 degrees 35 minutes for the inclination of the ecliptic. Rather than relying purely on Ptolemy's geometric constructions, al-Battani applied trigonometric methods to astronomical calculation, an important advance in how positions and motions were computed. His major compendium of astronomical tables was later translated into Latin around 1116 and into Spanish in the 13th century, with a printed edition appearing in 1537.

Why it matters

Al-Battani's corrections to Ptolemy's figures for the solar year and the precession of the equinoxes were accurate enough that they were still being used and cited by European astronomers centuries later, and his shift toward trigonometric methods pushed astronomical calculation away from pure geometric construction. His tables' translation into Latin and Spanish gave medieval and Renaissance European astronomers direct access to more accurate Islamic-era observational data.

How we know

Al-Battani's own astronomical compendium survives in Arabic manuscript and in its medieval Latin and Spanish translations, letting historians directly verify his stated observation dates, star catalog entries, and calculated values against the original text.

Sources

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