Ancient Greek astronomy was a significant field of study that emerged around the 6th century BCE. Greek astronomers, such as Ptolemy and Aristarchus, made important contributions by observing celestial bodies and developing models to explain their movements. They introduced concepts like the geocentric model, which placed the Earth at the center of the universe, and later, the heliocentric model proposed by Aristarchus, which suggested that the Sun was at the center. The Greeks also created tools for astronomical observations, including the astrolabe and the armillary sphere. They divided the sky into constellations, many of which are still recognized today. Their work laid the foundation for later developments in astronomy during the Renaissance and beyond.