Al-Battani's tropical year and solar apogee motion

What was discovered

With his own observations over 40 years, he measured the tropical year as 365 d 5 h 46 min 24 s and found that the Sun's apogee had shifted since Ptolemy's time. His Zij, translated into Latin, was a reference work for Copernicus and Tycho.

Copernicus cites him 23 times in De revolutionibus.

What it led to

• precise value of the year for calendar reform
• correction of Ptolemy's parameters
• Latin astronomical tables

Built on

• Almagest and Ptolemy theoremc. 150 CE
• Islamic astronomy and the Zij tablesc. 830

Made possible

• Jalali calendar1079

Links