This is a 1538 edition of one of the most influential works on astronomy of all time, the Almagest of Claudius Ptolemy.

Born in Egypt in the second century AD, Ptolemy is perhaps one of the greatest scientists of the ancient world. Very few details of his life are known aside from the belief that he spent most, if not all, of it in Alexandria. The Almagest was his greatest work and survived antiquity through its influence on astronomers throughout the Islamic world, eventually being translated into Latin in the 12th century. It remained the principal astronomical text through to the publication of Copernicus' De revolutionibus orbium coelestium in 1543.

The core belief in the Almagest is that the solar system was geocentric, meaning that the cosmos orbited the Earth. To justify this, Ptolemy theorized the Earth itself did not move, but that the Sun, Moon, stars and other planets were fixed to a celestial sphere which moved around the Earth day and night.