Geminus of

Rhodes Rhodes (; el, Ρόδος , translit=Ródos ) is the largest and the historical capital of the Dodecanese islands of Greece. Administratively, the island forms a separate municipality within the Rhodes regional unit, which is part of the S ...

( el, Γεμῖνος ὁ Ῥόδιος), was a

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

and

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, structure, space, models, and change. History On ...

, who flourished in the 1st century BC. An

astronomy Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, g ...

work of his, the ''Introduction to the Phenomena'', still survives; it was intended as an introductory astronomy book for students. He also wrote a work on

mathematics Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics ...

, of which only fragments quoted by later authors survive.

Life

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 the ''Annus Vagus'' (Wandering Year) of the

Egyptian calendar The ancient Egyptian calendar – a civil calendar – was a solar calendar with a 365-day year. The year consisted of three seasons of 120 days each, plus an intercalary month of five epagomenal days treated as outside of the year proper. Ea ...

of 120 years before his own time, has been used to imply a date of c. 70 BC for the time of writing, which would be consistent with the idea that he may have been a pupil of

Posidonius Posidonius (; grc-gre, Ποσειδώνιος , "of Poseidon") "of Apameia" (ὁ Ἀπαμεύς) or "of Rhodes" (ὁ Ῥόδιος) (), was a Greek politician, astronomer, astrologer, geographer, historian, mathematician, and teacher nativ ...

, but a date as late as 50 AD has also been suggested. The crater Geminus on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

is named after him.

Astronomy

The only work of Geminus to survive is his ''Introduction to the Phenomena'' ( el, Εἰσαγωγὴ εἰς τὰ Φαινόμενα), often just called the ''Isagoge''. This introductory astronomy book, based on the works of earlier astronomers such as

Hipparchus Hipparchus (; el, Ἵππαρχος, ''Hipparkhos''; BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the e ...

, was intended to teach astronomy for beginning students in the subject. In it, Geminus describes the

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the apparent path of the Sun across the celestial sphere over the course of the year. The pa ...

and the motion of the Sun, the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

s, the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphe ...

, days and nights, the risings and settings of the zodiacal signs, luni-solar periods and their application to calendars,

phases of the Moon Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...

eclipses An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three ce ...

, star phases, terrestrial zones and geographical places, and the foolishness of making weather predictions by the stars.Evans, J., ''The History and Practice of Ancient Astronomy'', p. 91. Oxford University Press. (1998). He also wrote a commentary on Posidonius' work ''On Meteorology''. Fragments of this commentary are preserved by Simplicius in his commentary on

Aristotle's Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...

''Physics''.

Mathematics

Geminus also wrote extensively on

, including a comprehensive ''Doctrine, (or Theory) of Mathematics.''Heath, T., A Manual of Greek Mathematics, Dover Publications. (2003). Although this work has not survived, many extracts are preserved by

Proclus Proclus Lycius (; 8 February 412 – 17 April 485), called Proclus the Successor ( grc-gre, Πρόκλος ὁ Διάδοχος, ''Próklos ho Diádokhos''), was a Greek Neoplatonist philosopher, one of the last major classical philosophe ...

Eutocius Eutocius of Ascalon (; el, Εὐτόκιος ὁ Ἀσκαλωνίτης; 480s – 520s) was a Palestinian-Greek mathematician who wrote commentaries on several Archimedean treatises and on the Apollonian ''Conics''. Life and work Little is ...

, and others. He divided mathematics into two parts: ''Mental'' ( el, νοητά) and ''Observable'' ( el, αἰσθητά), or in other words, Pure and Applied. In the first category he placed

geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of geometry is c ...

and

arithmetic Arithmetic () is an elementary part of mathematics that consists of the study of the properties of the traditional operations on numbers— addition, subtraction, multiplication, division, exponentiation, and extraction of roots. In the 19th ...

(including

number theory Number theory (or arithmetic or higher arithmetic in older usage) is a branch of pure mathematics devoted primarily to the study of the integers and integer-valued functions. German mathematician Carl Friedrich Gauss (1777–1855) said, "Ma ...

), and in the second category he placed

mechanics Mechanics (from Ancient Greek: μηχανική, ''mēkhanikḗ'', "of machines") is the area of mathematics and physics concerned with the relationships between force, matter, and motion among physical objects. Forces applied to objec ...

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

geodesy Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equival ...

, canonics ( musical harmony), and

logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...

. Long extracts of his work are also preserved by Al-Nayrizi in his commentary on Euclid's ''Elements''.

Notes

Bibliography

* Evans, J., Berggren, J.L.
''Geminos's Introduction to the Phenomena: A Translation and Study of a Hellenistic Survey of Astronomy.''
(Princeton University Press, 2006.)

External links

* ttps://archive.today/20020623142024/http://www.tmth.edu.gr/en/aet/2/49.html Technology Museum of Thessaloniki Entry*
PDF scans of Manitius' edition of the Geminus' ''Elementa Astronomiae'' ("Elements of Astronomy") – public domain
(Classical Greek with German translation)] {{DEFAULTSORT:Geminus Ancient Greek astronomers Ancient Greek mathematicians Ancient Rhodian scientists Roman-era Rhodians Stoic philosophers 1st-century BC Rhodians 1st-century BC writers 1st-century BC mathematicians