Greek astronomy is
astronomyAstronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
written in the
Greek languageGreek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
in
classical antiquityClassical antiquity is a broad term for a long period of cultural history centered on the Mediterranean Sea, comprising the interlocking civilizations of ancient Greece and ancient Rome, collectively known as the Greco-Roman world...
. Greek astronomy is understood to include the
ancient GreekAncient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...
,
HellenisticHellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BCE to about 146 BCE...
, Greco-Roman, and
Late AntiquityLate Antiquity is a periodization used by historians to describe the time of transition from Classical Antiquity to the Middle Ages, in both mainland Europe and the Mediterranean world. Precise boundaries for the period are a matter of debate, but noted historian of the period Peter Brown proposed...
eras. It is not limited geographically to
GreeceGreece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
or to ethnic Greeks, as the Greek language had become the language of scholarship throughout the Hellenistic world following the conquests of
Alexander. This phase of Greek astronomy is also known as
Hellenistic astronomy, while the pre-Hellenistic phase is known as
Classical Greek astronomy. During the Hellenistic and Roman periods, much of
the Greek and non-Greek astronomers working in the Greek tradition studied at the
MusaeumThe Musaeum or Mouseion at Alexandria , which included the famous Library of Alexandria, was an institution founded, according to Johannes Tzetzes, by Ptolemy I Soter or, perhaps more likely, by Ptolemy II Philadelphus at Hellenistic Alexandria in Egypt. The Mouseion remained supported by the...
and the
Library of AlexandriaThe Royal Library of Alexandria, or Ancient Library of Alexandria, in Alexandria, Egypt, was the largest and most significant great library of the ancient world. It flourished under the patronage of the Ptolemaic dynasty and functioned as a major center of scholarship from its construction in the...
in
Ptolemaic EgyptPtolemaic Egypt began when Ptolemy I Soter invaded Egypt and declared himself Pharaoh of Egypt in 305 BC and ended with the death of queen Cleopatra VII of Egypt and the Roman conquest in 30 BC. The Ptolemaic Kingdom was a powerful Hellenistic state, extending from southern Syria in the east, to...
.
The development of astronomy by the Greek and Hellenistic astronomers is considered by historians to be a major phase in the
history of astronomyAstronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, and astrological practices of pre-history: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy, and not...
. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. Most of the constellations of the northern hemisphere derive from Greek astronomy, as are the names of many stars and planets. It was influenced by Babylonian and, to a lesser extent,
Egyptian astronomyEgyptian astronomy begins in prehistoric times, in the Predynastic Period. In the 5th millennium BCE, the stone circles at Nabta Playa may have made use of astronomical alignments...
; in turn, it influenced Indian,
Arabic-IslamicIslamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...
and
Western EuropeWestern Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...
an astronomy.
Archaic Greek astronomy
References to identifiable
starA star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s and
constellationIn modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
s appear in the writings of
HomerIn the Western classical tradition Homer , is the author of the Iliad and the Odyssey, and is revered as the greatest ancient Greek epic poet. These epics lie at the beginning of the Western canon of literature, and have had an enormous influence on the history of literature.When he lived is...
and
HesiodHesiod was a Greek oral poet generally thought by scholars to have been active between 750 and 650 BC, around the same time as Homer. His is the first European poetry in which the poet regards himself as a topic, an individual with a distinctive role to play. Ancient authors credited him and...
, the earliest surviving examples of Greek literature. In the
IliadThe Iliad is an epic poem in dactylic hexameters, traditionally attributed to Homer. Set during the Trojan War, the ten-year siege of the city of Troy by a coalition of Greek states, it tells of the battles and events during the weeks of a quarrel between King Agamemnon and the warrior Achilles...
and the
OdysseyThe Odyssey is one of two major ancient Greek epic poems attributed to Homer. It is, in part, a sequel to the Iliad, the other work ascribed to Homer. The poem is fundamental to the modern Western canon, and is the second—the Iliad being the first—extant work of Western literature...
, Homer refers to the following celestial objects:
- the constellation Boötes
Boötes is a constellation in the northern sky, located between 0° and +60° declination, and 13 and 16 hours of right ascension on the celestial sphere. The name comes from the Greek Βοώτης, Boōtēs, meaning herdsman or plowman...
- the star cluster
Star clusters or star clouds are groups of stars. Two types of star clusters can be distinguished: globular clusters are tight groups of hundreds of thousands of very old stars which are gravitationally bound, while open clusters, more loosely clustered groups of stars, generally contain less than...
HyadesThe Hyades is the nearest open cluster to the Solar System and one of the best-studied of all star clusters. The Hipparcos satellite, the Hubble Space Telescope, and infrared color-magnitude diagram fitting have been used to establish a distance to the cluster's center of ~153 ly...
- the constellation Orion
Orion, often referred to as The Hunter, is a prominent constellation located on the celestial equator and visible throughout the world. It is one of the most conspicuous, and most recognizable constellations in the night sky...
- the star cluster Pleiades
In astronomy, the Pleiades, or Seven Sisters , is an open star cluster containing middle-aged hot B-type stars located in the constellation of Taurus. It is among the nearest star clusters to Earth and is the cluster most obvious to the naked eye in the night sky...
- Sirius
Sirius is the brightest star in the night sky. With a visual apparent magnitude of −1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Seirios . The star has the Bayer designation Alpha Canis Majoris...
, the Dog Star
- the constellation Ursa Major
Ursa Major , also known as the Great Bear, is a constellation visible throughout the year in most of the northern hemisphere. It can best be seen in April...
Hesiod, who wrote in the early 7th century BCE, adds the star
Arcturus to this list in his poetic calendar
Works and Days. Though neither Homer nor Hesiod set out to write a scientific work, they hint at a rudimentary
cosmologyCosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
of a
flat earthThe Flat Earth model is a belief that the Earth's shape is a plane or disk. Most ancient cultures have had conceptions of a flat Earth, including Greece until the classical period, the Bronze Age and Iron Age civilizations of the Near East until the Hellenistic period, India until the Gupta period ...
surrounded by an "
Ocean RiverOceanus ; , Ōkeanós) was a pseudo-geographical feature in classical antiquity, believed by the ancient Greeks and Romans to be the world-ocean, an enormous river encircling the world....
." Some stars rise and set (disappear into the ocean, from the viewpoint of the Greeks); others are
ever-visibleIn astronomy, circumpolar constellations are those that, from the viewer's latitude, never set. This is a very important effect to be considered in astronomy....
. At certain times of the year, certain stars will rise or set at sunrise or sunset.
Speculation about the
cosmosIn the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...
was common in
Pre-Socratic philosophyPre-Socratic philosophy is Greek philosophy before Socrates . In Classical antiquity, the Presocratic philosophers were called physiologoi...
in the 6th and 5th centuries BCE.
AnaximanderAnaximander was a pre-Socratic Greek philosopher who lived in Miletus, a city of Ionia; Milet in modern Turkey. He belonged to the Milesian school and learned the teachings of his master Thales...
(c. 610 BC–c. 546 BC) described a cylindrical earth suspended in the center of the cosmos, surrounded by rings of fire.
PhilolausPhilolaus was a Greek Pythagorean and Presocratic philosopher. He argued that all matter is composed of limiting and limitless things, and that the universe is determined by numbers. He is credited with originating the theory that the earth was not the center of the universe.-Life:Philolaus is...
(c. 480 BC–c. 405 BC) the
PythagoreanPythagoreanism was the system of esoteric and metaphysical beliefs held by Pythagoras and his followers, the Pythagoreans, who were considerably influenced by mathematics. Pythagoreanism originated in the 5th century BCE and greatly influenced Platonism...
described a cosmos with the stars, planets,
SunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
,
MoonThe Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
,
EarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
, and a counter-Earth (
AntichthonAntichthon is the journal of the Australasian Society for Classical Studies. The focus of the journal is Greece and Rome, however, its scope is broadly defined so as to embrace the Ancient Near East and the Mediterranean from the beginnings of civilisation to the Early Middle Ages....
)—ten bodies in all—circling an unseen central fire. Such reports show that Greeks of the 6th and 5th centuries BCE were aware of the planets and speculated about the structure of the cosmos.
The planets in early Greek astronomy
The name "planet" comes from the Greek term πλανήτης,
planētēs, meaning "wanderer", as ancient astronomers noted how certain lights moved across the sky in relation to the other stars. Five planets can be seen with the naked eye:
MercuryMercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
,
VenusVenus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...
,
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
,
JupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
, and
SaturnSaturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
. Sometimes the
luminariesThe luminaries were what traditional astrologers called the two astrological "planets" which were the brightest and most important objects in the heavens, that is, the Sun and the Moon.- Origins :...
, the Sun and Moon, are added to the list of naked eye planets to make a total of seven. Since the planets disappear from time to time when they approach the Sun, careful attention is required to identify all five.
Observations of VenusObservations of the planet Venus were first recorded by Babylonian astronomers around 1600 BC and have continued into the present. The Maya also kept records of the movements of Venus and attached special importance to the planet...
are not straightforward. Early Greeks thought that the evening and morning appearances of Venus represented two different objects, calling it
HesperusIn Greek mythology, Hesperus is the Evening Star, the planet Venus in the evening. He is the son of the dawn goddess Eos and is the brother of Eosphorus , the Morning Star. Hesperus' Roman equivalent is Vesper...
("evening star") when it appeared in the western evening sky and
Phosphorus ("light-bringer") when it appeared in the eastern morning sky. They eventually came to recognize that both objects were the same planet.
PythagorasPythagoras of Samos was an Ionian Greek philosopher, mathematician, and founder of the religious movement called Pythagoreanism. Most of the information about Pythagoras was written down centuries after he lived, so very little reliable information is known about him...
is given credit for this realization.
The planets eventually received names drawn from
Greek mythologyGreek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
. The equivalent names in
Roman mythologyRoman mythology is the body of traditional stories pertaining to ancient Rome's legendary origins and religious system, as represented in the literature and visual arts of the Romans...
are the basis for the modern English names of the planets.
Calendars
Many ancient calendars are based on the cycles of the Sun or Moon. The
Hellenic calendarThe Hellenic calendar—or more properly, the Hellenic calendars, for there was no uniform calendar imposed upon all of Classical Greece—began in most Greek states between Autumn and Winter except the Attic calendar, which began in June...
incorporated these cycles. A
lunisolar calendarA lunisolar calendar is a calendar in many cultures whose date indicates both the moon phase and the time of the solar year. If the solar year is defined as a tropical year then a lunisolar calendar will give an indication of the season; if it is taken as a sidereal year then the calendar will...
based on both cycles is difficult. Some Greek astronomers worked out calendars based on the
eclipse cycleEclipses may occur repeatedly, separated by certain intervals of time: these intervals are called eclipse cycles. The series of eclipses separated by a repeat of one of these intervals is called an eclipse series.- Eclipse conditions :...
.
Eudoxan astronomy
In classical Greece, astronomy was a branch of
mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
; astronomers sought to create geometrical models that could imitate the appearances of celestial motions. This tradition began with the Pythagoreans, who placed astronomy among the four mathematical arts (along with
arithmeticArithmetic or arithmetics is the oldest and most elementary branch of mathematics, used by almost everyone, for tasks ranging from simple day-to-day counting to advanced science and business calculations. It involves the study of quantity, especially as the result of combining numbers...
,
geometryGeometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....
, and
musicMusic is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...
). The study of
numberA number is a mathematical object used to count and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers....
comprising the four arts was later called the
quadriviumThe quadrivium comprised the four subjects, or arts, taught in medieval universities, after teaching the trivium. The word is Latin, meaning "the four ways" , and its use for the 4 subjects has been attributed to Boethius or Cassiodorus in the 6th century...
.
Although he was not a creative mathematician,
PlatoPlato , was a Classical Greek philosopher, mathematician, student of Socrates, writer of philosophical dialogues, and founder of the Academy in Athens, the first institution of higher learning in the Western world. Along with his mentor, Socrates, and his student, Aristotle, Plato helped to lay the...
(427–347 BCE) included the
quadrivium as the basis for philosophical education in the
Republic. He encouraged a younger mathematician,
Eudoxus of CnidusEudoxus of Cnidus was a Greek astronomer, mathematician, scholar and student of Plato. Since all his own works are lost, our knowledge of him is obtained from secondary sources, such as Aratus's poem on astronomy...
(c. 410 BCE–c. 347 BCE), to develop a system of Greek astronomy. According to a modern historian of science,
David LindbergDavid C. Lindberg is an American historian of science. His main focus is in the history of medieval and early modern science, especially physical science and the relationship between religion and science. Lindberg is the author or editor of many books and received numerous grants and awards...
:
- In their work we find (1) a shift from stellar to planetary concerns, (2) the creation of a geometrical model, the "two-sphere model," for the representation of stellar and planetary phenomena, and (3) the establishment of criteria governing theories designed to account for planetary observations. (Lindberg 1992, p. 90)
The
two-sphere model is a
geocentric modelIn astronomy, the geocentric model , is the superseded theory that the Earth is the center of the universe, and that all other objects orbit around it. This geocentric model served as the predominant cosmological system in many ancient civilizations such as ancient Greece...
. It divides the
cosmosIn the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...
into two regions:
- A spherical Earth, central and motionless (the sublunary sphere
The sublunary sphere is a concept derived from Greek astronomy. It is the region of the cosmos from the Earth to the Moon, consisting of the four classical elements: earth, water, air, and fire. Beginning with the Moon, up to the limits of the universe, everything is made of aether...
).
- A spherical heavenly realm centered on the Earth, which may contain multiple rotating spheres made of aether
According to ancient and medieval science aether , also spelled æther or ether, is the material that fills the region of the universe above the terrestrial sphere.-Mythological origins:...
Plato's main books on cosmology are the
TimaeusTimaeus is one of Plato's dialogues, mostly in the form of a long monologue given by the title character, written circa 360 BC. The work puts forward speculation on the nature of the physical world and human beings. It is followed by the dialogue Critias.Speakers of the dialogue are Socrates,...
and the
Republic. In them he described the two-sphere model and said there were eight circles or spheres carrying the seven planets and the fixed stars. He put the celestial objects in the following order, beginning with the one closest to Earth:
- Moon
- Sun
- Venus
- Mercury
- Mars
- Jupiter
- Saturn
- Fixed stars
According to the "
Myth of ErThe Myth of Er is an eschatological legend that concludes Plato's The Republic . The story includes an account of the cosmos and the afterlife that for many centuries greatly influenced religious, philosophical and scientific thought....
" in the
Republic, the cosmos is the Spindle of Necessity, attended by
SirenIn Greek mythology, the Sirens were three dangerous mermaid like creatures, portrayed as seductresses who lured nearby sailors with their enchanting music and voices to shipwreck on the rocky coast of their island. Roman poets placed them on an island called Sirenum scopuli...
s and spun by the three daughters of the Goddess Necessity known collectively as the
MoiraeThe Moirae, Moerae or Moirai , in Greek mythology, were the white-robed incarnations of destiny . Their number became fixed at three...
or Fates.
According to a story reported by
Simplicius of CiliciaSimplicius of Cilicia, was a disciple of Ammonius Hermiae and Damascius, and was one of the last of the Neoplatonists. He was among the pagan philosophers persecuted by Justinian in the early 6th century, and was forced for a time to seek refuge in the Persian court, before being allowed back into...
(6th century CE), Plato posed a question for the Greek mathematicians of his day: "By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?" (quoted in Lloyd 1970, p. 84). Plato proposed that the seemingly chaotic wandering motions of the planets could be explained by combinations of uniform circular motions centered on a spherical Earth, apparently a novel idea in the 4th century.
Eudoxus rose to the challenge by assigning to each planet a set of
concentricConcentric objects share the same center, axis or origin with one inside the other. Circles, tubes, cylindrical shafts, disks, and spheres may be concentric to one another...
spheres. By tilting the axes of the spheres, and by assigning each a different period of revolution, he was able to approximate the celestial "appearances." Thus, he was the first to attempt a mathematical description of the motions of the planets. A general idea of the content of
On Speeds, his book on the planets, can be gleaned from
AristotleAristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
's
MetaphysicsMetaphysics is one of the principal works of Aristotle and the first major work of the branch of philosophy with the same name. The principal subject is "being qua being", or being understood as being. It examines what can be asserted about anything that exists just because of its existence and...
XII, 8, and a commentary by Simplicius on
De caelo, another work by Aristotle. Since all his own works are lost, our knowledge of Eudoxus is obtained from secondary sources.
AratusAratus was a Greek didactic poet. He is best known today for being quoted in the New Testament. His major extant work is his hexameter poem Phaenomena , the first half of which is a verse setting of a lost work of the same name by Eudoxus of Cnidus. It describes the constellations and other...
's poem on
astronomyAstronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
is based on a work of Eudoxus, and possibly also
Theodosius of Bithynia'sTheodosius of Bithynia was a Greek astronomer and mathematician who wrote the Sphaerics, a book on the geometry of the sphere. Born in Tripolis, in Bithynia, Theodosius is cited by Vitruvius as having invented a sundial suitable for any place on Earth...
Sphaerics. They give us an indication of his work in
spherical astronomySpherical astronomy or positional astronomy is the branch of astronomy that is used to determine the location of objects on the celestial sphere, as seen at a particular date, time, and location on the Earth. It relies on the mathematical methods of spherical geometry and the measurements of...
as well as planetary motions.
CallippusCallippus or Calippus was a Greek astronomer and mathematician.Callippus was born at Cyzicus, and studied under Eudoxus of Cnidus at the Academy of Plato. He also worked with Aristotle at the Lyceum, which means that he was active in Athens prior to Aristotle's death in 322...
, a Greek astronomer of the 4th century, added seven spheres to Eudoxus' original 27 (in addition to the planetary spheres, Eudoxus included a sphere for the fixed stars). Aristotle described both systems, but insisted on adding "unrolling" spheres between each set of spheres to cancel the motions of the outer set. Aristotle was concerned about the physical nature of the system; without unrollers, the outer motions would be transferred to the inner planets.
Planetary models and observational astronomy
The Eudoxan system had several critical flaws. One was its inability to predict motions exactly. Callippus' work may have been an attempt to correct this flaw. A related problem is the inability of his models to explain why planets appear to change speed. A third flaw is its inability to explain changes in the brightness of planets as seen from Earth. Because the spheres are concentric, planets will always remain at the same distance from Earth. This problem was pointed out in Antiquity by
Autolycus of PitaneAutolycus of Pitane was a Greek astronomer, mathematician, and geographer. The lunar crater Autolycus was named in his honour.- Life and work :Autolycus was born in Pitane, a town of Aeolis within Western Anatolia...
(c. 310 BCE).
Apollonius of PergaApollonius of Perga [Pergaeus] was a Greek geometer and astronomer noted for his writings on conic sections. His innovative methodology and terminology, especially in the field of conics, influenced many later scholars including Ptolemy, Francesco Maurolico, Isaac Newton, and René Descartes...
(c. 262 BC–c. 190 BC) responded by introducing two new mechanisms that allowed a planet to vary its distance and speed: the
eccentricIn mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
deferent and the
deferent and epicycleIn the Ptolemaic system of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets...
. The
deferent is a circle carrying the planet around the Earth. (The word
deferent comes from the Latin
ferro, ferre, meaning "to carry.") An
eccentric deferent is slightly off-center from Earth. In a
deferent and epicycle model, the deferent carries a small circle, the
epicycle, which carries the planet. The deferent-and-epicycle model can mimic the eccentric model, as shown by
Apollonius' theorem. It can also explain retrogradation, which happens when planets appear to reverse their motion through the
zodiacIn astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
for a short time. Modern historians of astronomy have determined that Eudoxus' models could only have approximated retrogradation crudely for some planets, and not at all for others.
In the 2nd century BCE,
HipparchusHipparchus, the common Latinization of the Greek Hipparkhos, can mean:* Hipparchus, the ancient Greek astronomer** Hipparchic cycle, an astronomical cycle he created** Hipparchus , a lunar crater named in his honour...
, aware of the extraordinary accuracy with which Babylonian astronomers could predict the planets' motions, insisted that Greek astronomers achieve similar levels of accuracy. Somehow he had access to Babylonian observations or predictions, and used them to create better geometrical models. For the Sun, he used a simple eccentric model, based on observations of the equinoxes, which explained both changes in the speed of the Sun and differences in the lengths of the seasons. For the Moon, he used a
deferent and epicycleIn the Ptolemaic system of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets...
model. He could not create accurate models for the remaining planets, and criticized other Greek astronomers for creating inaccurate models.
Hipparchus also compiled a
star catalogueA star catalogue, or star catalog, is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, and this article covers only some...
. According to
Pliny the ElderGaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...
, he observed a
novaA nova is a cataclysmic nuclear explosion in a star caused by the accretion of hydrogen on to the surface of a white dwarf star, which ignites and starts nuclear fusion in a runaway manner...
(new star). So that later generations could tell whether other stars came to be, perished, moved, or changed in brightness, he recorded the position and brightness of the stars.
PtolemyClaudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...
mentioned the catalogue in connection with Hipparchus' discovery of precession. (
PrecessionPrecession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
of the equinoxes is a slow motion of the place of the equinoxes through the zodiac, caused by the shifting of the Earth's axis). Hipparchus thought it was caused by the motion of the sphere of fixed stars.
Heliocentrism and cosmic scales
In the 3rd century BCE,
Aristarchus of SamosAristarchus, or more correctly Aristarchos , was a Greek astronomer and mathematician, born on the island of Samos, in Greece. He presented the first known heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe...
proposed an alternate
cosmologyCosmology is the discipline that deals with the nature of the Universe as a whole. Cosmologists seek to understand the origin, evolution, structure, and ultimate fate of the Universe at large, as well as the natural laws that keep it in order...
(arrangement of the universe): a
heliocentricHeliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...
model of the
solar systemThe Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, placing the Sun, not the Earth, at the center of the known universe (hence he is sometimes known as the "Greek Copernicus"). His astronomical ideas were not well-received, however, and only a few brief references to them are preserved. We know the name of one follower of Aristarchus:
Seleucus of SeleuciaSeleucus of Seleucia was a Hellenistic astronomer and philosopher. Coming from Seleucia on the Tigris, the capital of the Seleucid empire, or, alternatively, Seleukia on the Red Sea, he is best known as a proponent of heliocentrism and for his theory of the origin of tides.- Heliocentric theory...
.
Aristarchus also wrote a book
On the Sizes and Distances of the Sun and MoonOn the Sizes and Distances is widely accepted as the only extant work written by Aristarchus of Samos, an ancient Greek astronomer who flourished circa 280–240 BC...
, which is his only work to have survived. In this work, he calculated the sizes of the Sun and Moon, as well as their distances from the Earth in
Earth radiiBecause the Earth is not perfectly spherical, no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km...
. Shortly afterwards,
EratosthenesEratosthenes of Cyrene was a Greek mathematician, poet, athlete, geographer, astronomer, and music theorist.He was the first person to use the word "geography" and invented the discipline of geography as we understand it...
calculated the size of the Earth, providing a value for the Earth radii which could be plugged into Aristarchus' calculations. Hipparchus wrote another book
On the Sizes and Distances of the Sun and MoonOn Sizes and Distances [of the Sun and Moon] is a text by the ancient Greek astronomer Hipparchus. It is not extant, but some of its contents have been preserved in the works of Ptolemy and his commentator Pappus of Alexandria...
, which has not survived. Both Aristarchus and Hipparchus drastically underestimated the distance of the Sun from the Earth.
Astronomy in the Greco-Roman and Late Antique eras
HipparchusHipparchus, the common Latinization of the Greek Hipparkhos, can mean:* Hipparchus, the ancient Greek astronomer** Hipparchic cycle, an astronomical cycle he created** Hipparchus , a lunar crater named in his honour...
is considered to have been among the most important Greek astronomers, because he introduced the concept of exact prediction into astronomy. He was also the last innovative astronomer before Claudius
PtolemyClaudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...
, a mathematician who worked at
AlexandriaAlexandria is the second-largest city of Egypt, with a population of 4.1 million, extending about along the coast of the Mediterranean Sea in the north central part of the country; it is also the largest city lying directly on the Mediterranean coast. It is Egypt's largest seaport, serving...
in
Roman EgyptThe Roman province of Egypt was established in 30 BC after Octavian defeated his rival Mark Antony, deposed his lover Queen Cleopatra VII and annexed the Ptolemaic kingdom of Egypt to the Roman Empire. The province encompassed most of modern-day Egypt except for the Sinai Peninsula...
in the 2nd century CE. Ptolemy's works on astronomy and
astrologyAstrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...
include the
AlmagestThe Almagest is a 2nd-century mathematical and astronomical treatise on the apparent motions of the stars and planetary paths. Written in Greek by Claudius Ptolemy, a Roman era scholar of Egypt,...
, the
Planetary Hypotheses, and the
TetrabiblosThe Tetrabiblos , also known under the Latin title Quadripartitum , is a text on the philosophy and practice of astrology, written in the second century AD by the Alexandrian scholar Claudius Ptolemy ....
, as well as the
Handy Tables, the
Canobic Inscription, and other minor works.
Ptolemaic astronomy
The
Almagest is one of the most influential books in the history of Western astronomy. In this book, Ptolemy explained how to predict the behavior of the planets, as Hipparchus could not, with the introduction of a new mathematical tool, the
equantEquant is a mathematical concept developed by Claudius Ptolemy in the 2nd century AD to account for the observed motion of heavenly bodies....
. The
Almagest gave a comprehensive treatment of astronomy, incorporating theorems, models, and observations from many previous mathematicians. This fact may explain its survival, in contrast to more specialized works that were neglected and lost. Ptolemy placed the planets in the order that would remain standard until it was displaced by the heliocentric system and the
Tychonic systemThe Tychonic system was a model of the solar system published by Tycho Brahe in the late 16th century which combined what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system...
:
- Moon
- Mercury
- Venus
- Sun
- Mars
- Jupiter
- Saturn
- Fixed stars
The extent of Ptolemy's reliance on the work of other mathematicians, in particular his use of Hipparchus' star catalogue, has been debated since the 19th century. A controversial claim was made by Robert R. Newton in the 1970s. in
The Crime of Claudius Ptolemy, he argued that Ptolemy faked his observations and falsely claimed the catalogue of Hipparchus as his own work. Newton's theories have not been adopted by most historians of astronomy.
A few mathematicians of Late Antiquity wrote commentaries on the
Almagest, including
Pappus of AlexandriaPappus of Alexandria was one of the last great Greek mathematicians of Antiquity, known for his Synagoge or Collection , and for Pappus's Theorem in projective geometry...
as well as
Theon of AlexandriaTheon was a Greek scholar and mathematician who lived in Alexandria, Egypt. He edited and arranged Euclid's Elements and Ptolemy's Handy Tables, as well as writing various commentaries...
and his daughter Hypatia. Ptolemaic astronomy became standard in medieval western European and
Islamic astronomyIslamic astronomy or Arabic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age , and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and...
until it was displaced by
MaraghanMaragheh observatory is an astronomical observatory which was established in 1259 CE by Nasir al-Din al-Tusi, an Iranian scientist and astronomer...
,
heliocentricHeliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...
and
Tychonic systemThe Tychonic system was a model of the solar system published by Tycho Brahe in the late 16th century which combined what he saw as the mathematical benefits of the Copernican system with the philosophical and "physical" benefits of the Ptolemaic system...
s by the 16th century. However, recently discovered manuscripts reveal that Greek astrologers of Antiquity continued using pre-Ptolemaic methods for their calculations (Aaboe, 2001).
Influence on Indian astronomy
HellenisticHellenistic civilization represents the zenith of Greek influence in the ancient world from 323 BCE to about 146 BCE...
astronomy is known to have been practiced near India in the
Greco-BactrianThe Greco-Bactrian Kingdom was the easternmost part of the Hellenistic world, covering Bactria and Sogdiana in Central Asia from 250 to 125 BC...
city of
Ai-KhanoumAi-Khanoum or Ay Khanum , was founded in the 4th century BC, following the conquests of Alexander the Great and was one of the primary cities of the Greco-Bactrian kingdom...
from the 3rd century BCE. Various sun-dials, including an equatorial sundial adjusted to the latitude of
UjjainUjjain , is an ancient city of Malwa region in central India, on the eastern bank of the Kshipra River , today part of the state of Madhya Pradesh. It is the administrative centre of Ujjain District and Ujjain Division.In ancient times the city was called Ujjayini...
have been found in archaeological excavations there. Numerous interactions with the Mauryan Empire, and the later expansion of the
Indo-GreeksThe Indo-Greek Kingdom or Graeco-Indian Kingdom covered various parts of the northwest regions of the Indian subcontinent during the last two centuries BC, and was ruled by more than 30 Hellenistic kings, often in conflict with each other...
into India suggest that some transmission may have happened during that period.
Several Greco-Roman astrological treatises are also known to have been imported into India during the first few centuries of our era. The
YavanajatakaThe Yavanajātaka of Sphujidhvaja is an ancient text in Indian astrology....
("Sayings of the Greeks") was translated from Greek to Sanskrit by
YavanesvaraYavaneśvara, Sanskrit for "Lord" "of the Greeks" , was a man who lived in the Gujarat region of India under the rule of the Western Kshatrapa Saka king Rudrakarman I....
during the 2nd century CE, under the patronage of the Western Satrap
SakaThe Saka were a Scythian tribe or group of tribes....
king
Rudradaman IRudradaman I was a Saka ruler from the Western Kshatrapas dynasty. He was the grandson of the celebrated Sah king Chastana. Rudradaman I was instrumental in the decline of the Satavahana Empire.- Mahakshatrapa :...
. Rudradaman's capital at Ujjain "became the Greenwich of Indian astronomers and the Arin of the Arabic and Latin astronomical treatises; for it was he and his successors who encouraged the introduction of Greek horoscopy and astronomy into India."
Later in the 6th century, the
Romaka SiddhantaThe Romaka Siddhanta is an Indian astronomical treatise, based on the astronomical learning of Byzantine Rome...
("Doctrine of the Romans"), and the
Paulisa SiddhantaThe Paulisa Siddhanta refers to multiple Indian astronomical treatises, at least one of which is based on a Western source. "Siddhanta" literally means "Doctrine" or "Tradition"....
("Doctrine of
PaulPaulus Alexandrinus was an astrological author from the late Roman Empire. His extant work, Eisagogika, or Introductory Matters , which was written in 378 CE, is a treatment of major topics in astrology as practiced in the fourth century Roman Empire.Little is known about Paulus' life...
") were considered as two of the five main astrological treatises, which were compiled by
VarahamihiraVarāhamihira , also called Varaha or Mihira, was an Indian astronomer, mathematician, and astrologer who lived in Ujjain...
in his
Pañca-siddhāntikā ("Five Treatises"). Varahamihira wrote in the Brihat-Samhita: "The Greeks, though impure, must be honored since they were trained in sciences and therein, excelled others....." The
Garga SamhitaGarga Samhita is a book written by the sage Garga and deals with the life of Krishna. This Garga Samhita is different from the astrological treatise with the same name Garga Samhita. Only fragments of the astrological text with the name Garga samhita is available; but the whole of the devotional...
also says: "The
Yavanas"Yona" is a Pali word used in ancient India to designate Greek speakers. Its equivalent in Sanskrit, Malayalam, Kannada, Telugu and Tamil is the word "Yavana" and "Jobonan/Jubonan" in Bengali...
are
barbarianBarbarian and savage are terms used to refer to a person who is perceived to be uncivilized. The word is often used either in a general reference to a member of a nation or ethnos, typically a tribal society as seen by an urban civilization either viewed as inferior, or admired as a noble savage...
s, yet the science of astronomy originated with them and for this they must be reverenced like gods."
Sources for Greek astronomy
Many Greek astronomical texts are known only by name, and perhaps by a description or quotations. Some elementary works have survived because they were largely non-mathematical and suitable for use in schools. Books in this class include the
Phaenomena of
EuclidEuclid , fl. 300 BC, also known as Euclid of Alexandria, was a Greek mathematician, often referred to as the "Father of Geometry". He was active in Alexandria during the reign of Ptolemy I...
and two works by
Autolycus of PitaneAutolycus of Pitane was a Greek astronomer, mathematician, and geographer. The lunar crater Autolycus was named in his honour.- Life and work :Autolycus was born in Pitane, a town of Aeolis within Western Anatolia...
. Three important textbooks, written shortly before Ptolemy's time, were written by
CleomedesCleomedes was a Greek astronomer who is known chiefly for his book On the Circular Motions of the Celestial Bodies.-Placing his work chronologically:...
,
GeminusGeminus of Rhodes , was a Greek astronomer and mathematician, who flourished in the 1st century BC. An astronomy 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, of which only...
, and
Theon of SmyrnaTheon of Smyrna was a Greek philosopher and mathematician, whose works were strongly influenced by the Pythagorean school of thought. His surviving On Mathematics Useful for the Understanding of Plato is an introductory survey of Greek mathematics.-Life:Little is known about the life of Theon of...
. Books by Roman authors like Pliny the Elder and
VitruviusMarcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....
contain some information on Greek astronomy. The most important primary source is the
Almagest, since Ptolemy refers to the work of many of his predecessors (Evans 1998, p. 24).
Famous astronomers of antiquity
In addition to the authors named in the article, the following list of people who worked on mathematical astronomy or cosmology may be of interest.
- Anaxagoras
Anaxagoras was a Pre-Socratic Greek philosopher. Born in Clazomenae in Asia Minor, Anaxagoras was the first philosopher to bring philosophy from Ionia to Athens. He attempted to give a scientific account of eclipses, meteors, rainbows, and the sun, which he described as a fiery mass larger than...
- Archimedes
Archimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...
- Archytas
Archytas was an Ancient Greek philosopher, mathematician, astronomer, statesman, and strategist. He was a scientist of the Pythagorean school and famous for being the reputed founder of mathematical mechanics, as well as a good friend of Plato....
- Aristaeus
Aristaeus the Elder was a Greek mathematician who worked on conic sections. He was a contemporary of Euclid, though probably older. We know practically nothing of his life except that the mathematician Pappus of Alexandria refers to him as Aristaeus the Elder which presumably means that Pappus was...
- Aristillus
Aristillus was a Greek astronomer, presumably of the school of Timocharis . He was among the earliest meridian-astronomy observers....
- Conon of Samos
Conon of Samos was a Greek astronomer and mathematician. He is primarily remembered for naming the constellation Coma Berenices.-Life and work:...
- Democritus
Democritus was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated an atomic theory for the cosmos....
- Empedocles
Empedocles was a Greek pre-Socratic philosopher and a citizen of Agrigentum, a Greek city in Sicily. Empedocles' philosophy is best known for being the originator of the cosmogenic theory of the four Classical elements...
- Heraclides Ponticus
Heraclides Ponticus , also known as Herakleides and Heraklides of Pontus, was a Greek philosopher and astronomer who lived and died at Heraclea Pontica, now Karadeniz Ereğli, Turkey. He is best remembered for proposing that the earth rotates on its axis, from west to east, once every 24 hours...
- Hicetas
Hicetas was a Greek philosopher of the Pythagorean School. He was born in Syracuse. Like his fellow Pythagorean Ecphantus and the Academic Heraclides Ponticus, he believed that the daily movement of permanent stars was caused by the rotation of the Earth around its axis....
- Hippocrates of Chios
Hippocrates of Chios was an ancient Greek mathematician, , and astronomer, who lived c. 470 – c. 410 BCE.He was born on the isle of Chios, where he originally was a merchant. After some misadventures he went to Athens, possibly for litigation...
- Macrobius
- Martianus Capella
Martianus Minneus Felix Capella was a pagan writer of Late Antiquity, one of the earliest developers of the system of the seven liberal arts that structured early medieval education...
- Menelaus of Alexandria
Menelaus of Alexandria was a Greek mathematician and astronomer, the first to recognize geodesics on a curved surface as natural analogs of straight lines.-Life and Works:...
(Menelaus theorem)
- Meton of Athens
Meton of Athens was a Greek mathematician, astronomer, geometer, and engineer who lived in Athens in the 5th century BC. He is best known for calculations involving the eponymous 19-year Metonic cycle which he introduced in 432 BC into the lunisolar Attic calendar.The metonic calendar assumes...
- Parmenides
Parmenides of Elea was an ancient Greek philosopher born in Elea, a Greek city on the southern coast of Italy. He was the founder of the Eleatic school of philosophy. The single known work of Parmenides is a poem, On Nature, which has survived only in fragmentary form. In this poem, Parmenides...
- Porphyry
Porphyry of Tyre , Porphyrios, AD 234–c. 305) was a Neoplatonic philosopher who was born in Tyre. He edited and published the Enneads, the only collection of the work of his teacher Plotinus. He also wrote many works himself on a wide variety of topics...
- Posidonius
Posidonius "of Apameia" or "of Rhodes" , was a Greek Stoic philosopher, politician, astronomer, geographer, historian and teacher native to Apamea, Syria. He was acclaimed as the greatest polymath of his age...
- Proclus
Proclus Lycaeus , called "The Successor" or "Diadochos" , was a Greek Neoplatonist philosopher, one of the last major Classical philosophers . He set forth one of the most elaborate and fully developed systems of Neoplatonism...
- Thales
Thales of Miletus was a pre-Socratic Greek philosopher from Miletus in Asia Minor, and one of the Seven Sages of Greece. Many, most notably Aristotle, regard him as the first philosopher in the Greek tradition...
- Theodosius of Bithynia
Theodosius of Bithynia was a Greek astronomer and mathematician who wrote the Sphaerics, a book on the geometry of the sphere. Born in Tripolis, in Bithynia, Theodosius is cited by Vitruvius as having invented a sundial suitable for any place on Earth...
See also
- Antikythera Mechanism
The Antikythera mechanism is an ancient mechanical computer designed to calculate astronomical positions. It was recovered in 1900–1901 from the Antikythera wreck. Its significance and complexity were not understood until decades later. Its time of construction is now estimated between 150 and 100...
- Greek mathematics
Greek mathematics, as that term is used in this article, is the mathematics written in Greek, developed from the 7th century BC to the 4th century AD around the Eastern shores of the Mediterranean. Greek mathematicians lived in cities spread over the entire Eastern Mediterranean, from Italy to...
- History of astronomy
Astronomy is the oldest of the natural sciences, dating back to antiquity, with its origins in the religious, mythological, and astrological practices of pre-history: vestiges of these are still found in astrology, a discipline long interwoven with public and governmental astronomy, and not...
- Babylonian influence on Greek astronomy
According to Asger Aaboe, the origins of Western astronomy can be found in Mesopotamia, and all Western efforts in the exact sciences are descendants in direct line from the work of the late Babylonian astronomers. Our knowledge of Sumerian astronomy is indirect, via the earliest Babylonian star...
External links