Sosigenes of Alexandria was named by Pliny the Elder

Pliny the Elder

Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

 as the astronomer

Astronomer

An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

 consulted by Julius Caesar

Julius Caesar

Gaius Julius Caesar was a Roman general and statesman and a distinguished writer of Latin prose. He played a critical role in the gradual transformation of the Roman Republic into the Roman Empire....

 for the design of the Julian calendar

Julian calendar

The Julian calendar began in 45 BC as a reform of the Roman calendar by Julius Caesar. It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the tropical year .The Julian calendar has a regular year of 365 days divided into 12 months...

.

Little is known about him apart from Pliny's Natural History. Sosigenes appears in Book 18, 210-212:

"... There were three main schools, the Chaldaean, the Egyptian, and the Greek; and to these a fourth was added in our country by Caesar during his dictatorship, who with the assistance of the learned astronomer Sosigenes (Sosigene perito scientiae eius adhibito) brought the separate years back into conformity with the course of the sun."

In Book 2, chapter 6, Sosigenes is credited with work on the orbit of Mercury

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...

:

"The star next to Venus is Mercury, by some called Apollo; it has a similar orbit, but is by no means similar in magnitude or power. It travels in a lower circle, with a revolution nine days quicker, shining sometimes before sunrise and sometimes after sunset, but according to Cidenas and Sosigenes never more than 22 degrees away from the sun."

Some sources state that the Julian calendar was designed by Aristarchus of Samos

Aristarchus of Samos

Aristarchus, or more correctly Aristarchos , was a Greek astronomer and mathematician, born on the island of Samos, in Greece. He presented the first known heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe...

; it is not clear where this originates, although a reform of the Egyptian calendar

Egyptian calendar

The ancient civil Egyptian calendar had a year that was 360 days long and was divided into 12 months of 30 days each, plus five extra days at the end of the year. The months were divided into three weeks of ten days each...

 was decreed by Ptolemy III Euergetes

Ptolemy III Euergetes

-Family:Euergetes was the eldest son of Ptolemy II Philadelphus and his first wife, Arsinoe I, and came to power in 246 BC upon the death of his father.He married Berenice of Cyrene in the year corresponding to 244/243 BC; and their children were:...

 in 238 BC, but never implemented.

Sosigenes was portrayed by Hume Cronyn

Hume Cronyn

Hume Blake Cronyn, OC was a Canadian actor of stage and screen, who enjoyed a long career, often appearing professionally alongside his second wife, Jessica Tandy.-Early life:...

 in Cleopatra

Cleopatra (1963 film)

Cleopatra is a 1963 British-American-Swiss epic drama film directed by Joseph L. Mankiewicz. The screenplay was adapted by Sidney Buchman, Ben Hecht, Ranald MacDougall, and Mankiewicz from a book by Carlo Maria Franzero. The film starred Elizabeth Taylor, Richard Burton, Rex Harrison, Roddy...

.