Very little is known about the life of Oenopides of Chios. He travelled to Egypt and acquired skills in astronomy. Oennopides his work focused on studies of the solar and lunar years. The discoveries Oenopides made were written on a bronze tablet which was offered to Olympia.

A major contribution said to be made by Oenopides to mathematical astronomy was his discovery of the period of the Great Year. At first the "Great Year" is the time it takes for the sun and moon to return to their starting point. afterwards it meant the time it takes for the motion of the moon, sun and planets to repeat themselves. In other words: after one Great Year all planets should have returned to their starting position at of the beginning of the Great Year.

Based on this some say that Oenopides's result leads to 29.53013 days for a lunar month, which is very close to the value of 29.53059 days that is used nowadays. Other doubt that Oenopides made the contributions all by himself, but with the help of others.