Euctemon in Wikipedia

Euctemon (unknown-fl. 432 BC) was an Athenian astronomer. He was a contemporary of Meton and worked closely with this astronomer. Little is known of his work apart from his partnership with Meton and what is mentioned by Ptolemy. With Meton, he made a series of observations of the solstices (the points at which the sun is at greatest distance from the equator) in order to determine the length of the tropical year. Geminus and Ptolemy quote him as a source on the rising and setting of the stars. The lunar crater Euctemon is named after him.