Cleostratus of Tenedos (Κλεόστρατος ὁ Τενήδιος) was an early Greek astronomer from the island of Tenedos, active in the late 6th or early 5th century BCE [1]. He is credited with introducing the constellations Aries and Sagittarius into Greek astronomy and with developing the eight-year lunisolar calendrical cycle known as the octaeteris, a system later refined by Meton and Euctemon [1]. Ancient sources suggest his work may reflect Babylonian influence, positioning him in a transitional phase between mythological cosmologies and systematic astronomy [1].

Works His lost works include the Astronomia (Ἀστρονομία), on constellations and celestial phenomena, and the Phainomena (Φαινόμενα), a title commonly used for works describing stellar appearances and weather signs [1].

Significance Cleostratus helped standardize the Greek celestial map, providing a foundation for later astronomical tradition. His practical work on the octaeteris represents a significant early effort to create a reliable calendar based on astronomical observation [1].

Sources 1. Encyclopædia Britannica: https://www.britannica.com/biography/Cleostratus-of-Tenedos