Sosigenes of Alexandria was named by Pliny the Elder as the astronomer consulted by Julius Caesar for the design of the Julian calendar. It appears that little or nothing is known about him apart from two references in Pliny's Natural History. Some web sources say that the calendar was designed by Aristarchus about 200 years earlier - it is not clear where this idea originates, although various reforms had been proposed around this time for the Egyptian administrative calendar. Like the Julian calendar, this had a standard year of 365 days divided into 12 months, but lacked a leap year. Pliny the Elder: an imaginative 19c portrait. ... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ... Bust of Julius Caesar Gaius Julius Caesar (Classical Latin: IMP·C·IVLIVS·CAESAR·DIVVS¹) (b. ... The Julian calendar was introduced in 46 BC by Julius Caesar and took force in 45 BC (709 ab urbe condita). ... Naturalis Historia Pliny the Elders Natural History is an encyclopedia written by Pliny the Elder. ... Aristarchus (310 BC - circa 230 BC) was a Greek astronomer and mathematician, born in Samos, Greece. ...

He appears in Pliny book 18, 210-212 (translation from [1]):

"... 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 Pliny book 2, 8, Sosigenes is credited with work on the orbit of Mercury (a very old translation from [2]): Atmospheric characteristics Atmospheric pressure trace Potassium 31. ...

"Next upon it, but nothing of that bignesse and powerfull efficacie, is the starre Mercurie, of some cleped Apollo: in an inferiour circle hee goeth, after the like manner, a swifter course by nine daies: shining sometimes before the sunne rising, otherwhiles after his setting, never farther distant from him than 23 degrees, as both the same Timæus and Sosigenes doe shew."

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