(fl. Rome, middle of first century b.c.)
Sosigenes helped Julius Caesar with his reform of the calendar. Caesar is said to have made use of Egyptian astronomy, but this may mean only that he discussed astronomy with Greeks from Alexandria. It is, in any case, not certain that Sosigenes was an Alexandrian, and he is not the only person whom Caesar consulted. Plutarch (Caesar, 59)simply states, without mentioning any names, that Caesar consulted the best philosophers and mathematicians before producing an improved calendar of his own. Caesar’s adoption of the 365–l/4–day solar year may have been one result of Sosigenes’advice, and the stateman’s seasonal calendar anoher. The 365–1/4–day year could even have been borrowed directly from Callippus at the suggestion of Sosigenes. All that Pliny says in this connection, however, is that during Caesar’s dictatorship Sosigenes helped him to bring the years back into conformity with the sun (Naturalis historia 18.211). He adds (Naturalis historia 18.212) that Sosigenes wrote three treatises, including corrections of his own statements.
Sosigenes agreed with Cidenas in giving the greatest elongation of Mercury from the sun as 22°(Piny,Naturalis historia 2.39). It is therefore possible, but far from certain, that he made use of Babylonian astronomical knowledge. Lucan (Pharsalia 10.187) implies that Caesar tried to improve upon the seasonal calendar of Eudoxus– “nec meus Eudoxi vincetur fastibus annus” (“and my year shall not be found inferior to the calendar of Eudoxus”). Theodor Mommsen maintains that Caesar “...with the help of the Greek mathematician Sosigenes introduced the Italian farmer’s year regulated according to the Egyptian calendar Eudoxus, as well as a rational system of intercalation, into religious and official use.” Mommsen here alludes to the calendar in the papyrus Ars Eudoxi, but there is no proof of any close connection between the ideas of Sosigenes and the doctrines in the Ars
On Caesar’s alleged use of “Egyptian”sources, see Appian, Bella civilia 2.154; Dio Cassius, Hist. Rom. 43.26; and Macrobius, Saturnalia 1.16.39 and 1.14.3. There are useful discussions regarding Caesar and Eudoxus’ seasonal calendar in A. Böckh, Ueber die vierjährige Sonnenkreise der Alten (Berlin. 1863), 340–342; F. K. Ginzel, Handbuch der mathematischen und technischen Chronologie, II (Leipzig, 1911), 274–277; and Pauly-Wissowa, Real-Encyclopädie, 2nd ser., III (Stuttgart, 1927) s.v. Sosigenes (b) 1153–1157–compare Theodor Mommsen, The Histry of Rome,IV (London, 1887),555. The calendar in the Ars Eudoxi is discussed in C. Wachsmuth, Ioannis Laurentii Lydi Liber de ostentis et calendaria Graeca omnia (Leipzig,1897), lxviii– lxix, 299–301.
G. L. Huxley