Geminus | |
|---|---|
Γεμῖνος ὁ Ῥόδιος | |
| Known for | Astronomer and mathematician |
| Scientific career | |
| Academic advisors | Posidonius |
Geminus ofRhodes (Greek:Γεμῖνος ὁ Ῥόδιος), was aGreekastronomer andmathematician, who flourished in the 1st century BC. Anastronomy work of his, theIntroduction to the Phenomena, still survives; it was intended as an introductory astronomy book for students. He also wrote a work onmathematics, of which only fragments quoted by later authors survive.
Nothing is known about the life of Geminus. It is not even certain that he was born in Rhodes, but references to mountains on Rhodes in his astronomical works suggests that he worked there. His dates are not known with any certainty either. A passage in his works referring to theAnnus Vagus (Wandering Year) of theEgyptian calendar of 120 years before his own time, has been used to imply a date of c. 70 BC for the time of writing,[1] which would be consistent with the idea that he may have been a pupil ofPosidonius, but a date as late as 50 AD has also been suggested.[2]
The craterGeminus on theMoon is named after him.[citation needed]
The only work of Geminus to survive is hisIntroduction to the Phenomena (Greek:Εἰσαγωγὴ εἰς τὰ Φαινόμενα), often just called theIsagoge. This introductory astronomy book, based on the works of earlier astronomers such asHipparchus, was intended to teach astronomy for beginning students in the subject. In it, Geminus describes thezodiac and the motion of theSun, theconstellations, thecelestial sphere, days and nights, the risings and settings of the zodiacal signs, luni-solar periods and their application tocalendars,phases of the Moon,eclipses, star phases, terrestrial zones and geographical places, and the foolishness of making weather predictions by the stars.[3]
He also wrote a commentary on Posidonius' workOn Meteorology. Fragments of this commentary are preserved bySimplicius in his commentary onAristotle'sPhysics.
Geminus also wrote extensively onmathematics, including a comprehensiveDoctrine, (or Theory) of Mathematics.[4] Although this work has not survived, many extracts are preserved byProclus,Eutocius, and others. He divided mathematics into two parts:Mental (Greek:νοητά) andObservable (Greek:αἰσθητά), or in other words,Pure andApplied. In the first category he placedgeometry andarithmetic (includingnumber theory), and in the second category he placedmechanics,astronomy,optics,geodesy, canonics (musical harmony), andlogistics. Long extracts of his work are also preserved byAl-Nayrizi in his commentary onEuclid'sElements.
