Callippus - The Ancient Greek Astronomer Who Revolutionized the Calendar

Callippus (Greek: Καλλίππος, Kallíppos) was a Greek astronomer and mathematician who lived in the 4th century BC. He was born in the island of Rhodes and studied under the famous philosopher and scientist Plato.

Callippus is best known for his work on the calendar, which he developed together with his teacher Plato and the mathematician Timaeus. This calendar, known as the Callippic cycle, was based on the idea that the solar year was not exactly 365 days long, but rather 365.242198 days long. To account for this discrepancy, the Callippic cycle introduced an extra month every few years, which was called the "intercalary" month.

Callippus also made other contributions to astronomy and mathematics, including the development of a new method for predicting eclipses and the calculation of the distance of the moon from the Earth. He is considered one of the most important figures in the history of ancient Greek astronomy and mathematics.