Astronomy · a Light

He measured the year and was off by two minutes

Al-Battani observed from Raqqa, on the Euphrates, from about 877 until 918, with instruments he had built and checked himself. He put the length of the solar year at 365 days, 5 hours, 46 minutes and 24 seconds, which is about two minutes and twenty seconds short of the modern value. He also found that the point at which the sun is furthest from the earth had shifted since Ptolemy recorded its position, which meant the Greek tables were not simply to be copied forward. His own tables were translated into Latin in the twelfth century, he was known in Europe as Albategnius, and Copernicus cites him repeatedly in the book of 1543. There is a crater on the moon carrying his Latin name.

Al-Battani · Raqqa, died 929 CE