Astronomy · a Light

A little cloud in his star book was another galaxy

In 964 the Persian astronomer Abd al-Rahman al-Sufi finished his Book of Fixed Stars in Isfahan. He went through Ptolemy's catalogue constellation by constellation, checked every star with his own eyes, corrected magnitudes and positions, drew each constellation twice, as seen on a globe and as seen in the sky, and recorded the Arabic names Bedouin observers already used. In Andromeda he described a small cloud, a faint patch that was not a star. It is the earliest known record of the Andromeda galaxy, which no one would understand as a separate galaxy until the 1920s. His book was copied and translated for six hundred years, and many star names in use today come through it.

Al-Sufi · Isfahan, 964 CE