First century B.C.

Greek astronomer who was among those consulted by Julius Caesar on calendar reform. Sources suggest that Sosigenes used Egyptian astronomical calculations, and was the person who convinced Caesar to use a 365-day year with a leap year every four years. He may have also been the one who suggested making the year 45 B.C. 445 days long to bring the seasons back in line with the calendar. He possibly wrote three books, but none survive.