Ancient Greek astronomy is the astronomy written in the Greek language during classical antiquity. Greek astronomy is understood to include the Ancient Greek, Hellenistic, Greco-Roman, and late antique eras. Ancient Greek astronomy can be divided into three phases, with Classical Greek astronomy being practiced during the 5th and 4th centuries BC, Hellenistic astronomy from the 3rd century BC until the formation of the Roman Empire in the late 1st century BC, and Greco-Roman astronomy continuing the tradition in the Roman world. During the Hellenistic era and onwards, Greek astronomy expanded beyond the geographic region of Greece as the Greek language had become the language of scholarship throughout the Hellenistic world, in large part delimited by the boundaries of the Macedonian Empire established by Alexander the Great. The most prominent and influential practitioner of Greek astronomy was Ptolemy, whose Almagest shaped astronomical thinking until the modern era. Most of the most prominent constellations known today are taken from Greek astronomy, albeit via the terminology they took on in Latin.
Greek astronomy was influenced heavily by Babylonian astronomy, as well as Egyptian astronomy to a lesser degree. In later centuries, Greek-language astronomical works were translated into other languages, enabling their further spread. Most notably, Arabic translations of these works benefitted astronomers and mathematicians throughout the Muslim world during the Middle Ages.
