FlourishedRome, (Italy), middle of first century BCE

Sosigenes was a Greek or Egyptian astronomer and mathematician of the Alexandrian School, about whom little is known. He is known as the main astronomer who helped Julius Caesar with his reform of the Roman lunar calendar, although his role in this reform is not very clear.  Plutarch simply states, without mentioning any names, that Caesar consulted the best philosophers and mathematicians before making an improved calendar of his own. And all that  Pliny says is that during Caesar’s dictatorship Sosigenes helped him to bring the years back into conformity with the Sun. He adds that Sosigenes wrote three treatises, including corrections of his own statements. It is, in any case, not certain that Sosigenes was in Alexandria during Caesar’s stay in Egypt after the battle of Pharsalos.

Caesar had a genuine interest in astronomy and composed a treatise, De Astris, a kind of farmer’s almanac with a remarkable popularity, based on...