Complex sentence: The development of astronomy by the Greek and Hellenistic astronomers is considered by historians to be a major phase in the Egyptian and especially Babylonian astronomy; in turn, it influenced Indian, Arabic-Islamic and Western European astronomy.
Split into simpler sentences: The development of astronomy by the Greek and Hellenistic astronomers is considered by historians to be a major phase in the history of astronomy. It was influenced by Egyptian and especially Babylonian astronomy; in turn, it influenced Indian, Arabic-Islamic and Western European astronomy.