The "Almagest" is a seminal astronomical text written by the ancient Greek astronomer Claudius Ptolemy in the 2nd century. It serves as a comprehensive guide to the geocentric model of the universe, where Earth is at the center, and it details the movements of celestial bodies, including the Sun, Moon, and planets. This work was influential for many centuries, shaping the understanding of astronomy in the Western and Islamic worlds. The "Almagest" includes mathematical models and star catalogs, making it a foundational text for later astronomers and scholars, including Copernicus and Kepler.