Flourished(Greece), circa432 BCE
Almost nothing is known of the Greek astronomer Euctemon, including his birth and death dates; it is known that he worked with the astronomer Meton in Athens around 432 BCE. This bit of information comes to us from Ptolemy , who mentions Meton and Euctemon. There is also a reference to Euctemon in Pausanius’ Description of Greece as being the father of Damon and Philogenes, two Athenians who provided ships to the Ionians for their voyage to Asia. One reference indicates that Euctemon was wealthy enough to have craftsmen working for him.
Euctemon’s chief astronomical contributions were largely in conjunction with those of Meton. They were reported to have developed a calendar of 365.25 + 1/76 of a day (30 min too long). A 19-year cycle was developed from an observation of the solstices since it was similar to observations made earlier in Mesopotamia, although the independent nature of the discovery is suspect. The Metonic cycle arises from 19 solar years, being almost exactly equal to 235 lunar cycles, and allows the prediction of eclipses. They also noted the inequality in the lengths of the seasons. Euctemon and Meton are also known for having introduced the parapegma, which was a tool used to associate the rising of a particular star and the civil calendar date. The parapegma was a stone tablet with movable pegs and inscriptions that allowed for such a calculation. A crater on the Moon is named for Euctemon.