Ancient Greek Astronomy

Ancient Greek astronomy covers the sky-watching recorded in Greek from the Classical age into the Roman world. Small-group trips through Greece run from Athens to Rhodes and Samos. The topics include the Antikythera mechanism, Hipparchus, the Almagest and Aristarchus of Samos. Later topics take in the Metonic cycle, the Attic calendar, the Pleiades and the Tower of the Winds. Further reading sits in Ancient Greek inventions, Museums in Greece and Ancient Greek philosophers. All other trips are gathered under Greece tours.

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What was ancient Greek astronomy?

Ancient Greek astronomy is the study of the sky set down in Greek across classical antiquity. Scholars split it into three phases: Classical, Hellenistic and Greco-Roman. Babylonian work shaped it heavily, while Egyptian work shaped it to a lesser degree.

Classical Greek astronomy belonged to the 5th and 4th centuries BC. A Hellenistic phase followed from the 3rd century BC. It lasted until the Roman Empire took shape in the late 1st century BC. Greek by then served as the language of scholarship across the Hellenistic world. The Greco-Roman phase continued ancient Greek astronomy inside the Roman world.

Archaic Greek thought pictured a flat Earth, with an outer ocean circling the lands where people lived. The word planet comes from a Greek term for wanderer. Certain points of light moved against the fixed stars. Five planets are visible to the naked eye. Ancient Greek astronomy called them Hermes, Aphrodite, Ares, Zeus and Cronus.

Early Greek observers took the evening and morning appearances of Venus for two separate bodies. They named the evening one Hesperus and the morning one Phosphorus, the light-bringer. Credit for seeing both as one planet goes to Pythagoras or Parmenides. Arabic translations of Greek works later served medieval scholars across the Muslim world.

• Constellations: Leading star patterns known today come from Greek astronomy, with their names passing through Latin.
• Textbooks: Cleomedes, Geminus and Theon of Smyrna wrote three key textbooks shortly before the time of Ptolemy.
• Ecliptic: This term means the yearly path of the Sun, tilted 23 degrees from the sky’s equator.

Plato and Eudoxus of Cnidus moved ancient Greek astronomy from the stars towards the planets. Their shift dates to the earlier half of the fourth century BC. A new two-sphere model set a fixed Earth inside the sphere of the heavens.

What did the Antikythera mechanism calculate for ancient Greek astronomy?

Ancient Greek astronomy reached a mechanical form in the Antikythera mechanism. Its rear face carried a spiral dial for eclipses. This Saros dial followed a cycle of 223 lunar months. Symbols in 51 of its cells marked 38 lunar and 27 solar eclipses.

The Saros cycle lasts 18 years and 11 and one-third days, and it repeats eclipse conditions. Its extra third of a day pushes each eclipse eight hours later. A smaller dial below tracked the exeligmos, a triple Saros of 54 years. That longer cycle of ancient Greek astronomy ran to 19,756 days and returned to whole days.

Mechanical engineer Michael Wright showed that the device displayed the phase of the Moon. A small ball sat in the lunar pointer, half white and half black. It turned to show each phase, from new moon to full moon. The display needed a differential gear, which adds or subtracts two turning motions.

The upper right dial linked ancient Greek astronomy to the Panhellenic Games, contests shared across the Greek world. Its pointer alone moved anticlockwise as time advanced. Four sectors named the crown games of Isthmia, Olympia, Nemea and Pythia. Two lesser contests also appeared: Naa at Dodona and the Halieia of Rhodes.

• Manual: The back door of the wooden case appears to serve as an instruction manual.
• Fragment 19: Its text records 76 years and 19 years, the Callippic and Metonic cycles.
• Crank: One full turn of the crank shifted the date pointer by about 78 days.

A 2017 study by Iversen traced the prototype for this piece of ancient Greek astronomy to Rhodes. The same study held that a client in Epirus, in northwestern Greece, received this adapted model. Its date falls no more than a generation before the shipwreck.

Why does Hipparchus stand out in ancient Greek astronomy?

Ancient Greek astronomy counts Hipparchus as its greatest observer. His numerical models of the Sun and Moon are the earliest accurate ones to survive. He is best known for finding the precession of the equinoxes, a slow drift in their positions.

He appears to be the first astronomer to use Babylonian methods systematically. He tested his results against Babylonian eclipse records 345 years older than his own. Meton’s solstice observation lay 297 years, or 108,478 days, before his own. That span gave ancient Greek astronomy a tropical year, the cycle of seasons, just under 365.25 days.

Astronomers before him knew that the seasons differ in length. A Sun moving at an even speed in a circle around the Earth cannot produce that result. Hipparchus answered by placing the Earth away from the centre of the solar path. Pliny the Elder also records that he observed a nova, a new star.

Late in his career, possibly about 135 BC, he compiled a catalogue of stars. Ptolemy later absorbed it into his own list. Subtracting two and two-thirds degrees from Ptolemy’s east-west star positions nearly rebuilds it. Ancient Greek astronomy also gained from him a globe of the sky showing the constellations.

• Equatorial ring: The ring casts its shadow onto itself at the moment the Sun crosses the equator.
• Alexandria: Ptolemy quotes a description by Hipparchus of one such ring in Alexandria.
• Sidereal year: His sidereal year, measured against the fixed stars, ran slightly over 365.25 days.

Hipparchus wrote at least fourteen books, yet only his commentary on a poem by Aratus survives. Knowledge of his other work in ancient Greek astronomy rests mainly on Strabo, Pliny and Ptolemy. He used observations made earlier by Meton, Timocharis, Aristyllus, Aristarchus and Eratosthenes.

How did the Almagest of Ptolemy shape ancient Greek astronomy?

Ancient Greek astronomy has a key source in the Almagest, a 2nd-century treatise on stars and planets. Claudius Ptolemy wrote it in Koine Greek, the common Greek of that era. Its Earth-centred model held sway for more than 1,200 years.

Ptolemy lived in or near Alexandria, then a city of Roman Egypt. Ancient Greek astronomy took more of his time than any other subject. About half his surviving works treat it. He set up a public inscription at Canopus in Egypt in 147 or 148. An earlier version of his models appears in that text.

The work holds thirteen sections called books, with roughly a quarter of a million words in Greek. Book VI treats eclipses of the Sun and Moon. Books VII and VIII list 1022 stars by their positions in the constellations. Ptolemy fitted these stars into the traditional scheme of 48 constellations of ancient Greek astronomy.

Its first name in Koine Greek was Mathematike Syntaxis, the Mathematical Treatise. Later readers called it the Great Treatise. The Greek word for greatest, megiste, lay behind its Arabic name. A Latin translation from the Arabic followed in the 12th century under the title Almagestum. Original Greek copies surfaced again in the 15th century.

• Oldest copies: The surviving text comes from copies, and the oldest date from the 9th century.
• Book III: Ptolemy explains there how Hipparchus discovered the precession of the equinoxes.
• Critic: Robert Newton argued in a 1977 book that Ptolemy invented data to fit his theories.

The first book sets out spherical heavens and a motionless, spherical Earth at the centre. Ancient Greek astronomy rested on those assumptions, and that book defends each one with philosophy and observation. Book II covers daylight, latitude and the shadows of a gnomon, a shadow-casting rod.

Where does Aristarchus of Samos stand in ancient Greek astronomy?

Ancient Greek astronomy gained its first known Sun-centred model from Aristarchus of Samos, born around 310 BC. His scheme had the Earth circling the Sun yearly and spinning on its axis daily. His ideas lost out to the Earth-centred theories of Aristotle and Ptolemy.

Ptolemy records that Aristarchus watched the summer solstice, the longest day of the year, in 280 BC. Two sundials are credited to him by Vitruvius, a flat disc and a hemisphere. Ancient Greek astronomy credits him with sizing the Sun at 7 times the Earth. In truth the solar diameter runs to 109 times that of the Earth.

The greater size of the Sun made it, for Aristarchus, the obvious middle point of the universe. He then set the remaining planets around the Sun in the right order. Ancient Greek astronomy recorded no stellar parallax, the apparent shift of a star as the Earth moves. Belief in the Earth-centred model lasted throughout the Middle Ages.

The claim that his contemporaries found the Sun-centred view sacrilegious, meaning offensive to religion, is a common error. Lucio Russo traces it to a printing by Gilles Ménage of a passage in Plutarch. In the original manuscript, Aristarchus jokes that Cleanthes, the Stoic leader, deserves a charge of impiety.

• Half moon: He put the Sun-Moon angle at half moon at 87 degrees, below the true value.
• Distances: He concluded that the Sun lay 18 to 20 times farther off than the Moon.
• Namesakes: His name lives on in a lunar crater, the Aristarchos telescope and minor planet 3999.

His book on the sizes and distances of Sun and Moon keeps to an Earth-centred view. Plutarch reports that he offered the Sun-centred idea of ancient Greek astronomy only as a hypothesis. Copernicus later revived the theory, and Kepler described the planetary motions more accurately.

Which calendar problem did the Metonic cycle solve in ancient Greek astronomy?

Ancient Greek astronomy used the Metonic cycle to match lunar phases to the seasons. After almost exactly 19 years, each phase returns at the same time of year. Meton of Athens set the cycle at 6,940 whole days in the 5th century BC.

A tropical year, set by the seasons, lasts about 365.24 days. Twelve lunar months fall short, and thirteen overshoot. Within this cycle of ancient Greek astronomy, twelve years hold 12 lunar months; seven hold 13. Whole numbers like these made a lunisolar calendar, following both Moon and Sun, easier to build.

A synodic month runs from one new moon to the next new moon. A span of 235 of them exceeds 19 tropical years by 2 hours, 4 minutes and 58 seconds. Of those months, 125 were full months of 30 days and 110 were short months of 29 days.

In ancient Greek astronomy, Meton added the cycle to the Attic calendar, that of Athens, in 432 BC. The Babylonians had applied a 19-year cycle from the late sixth century BC. Diodorus Siculus reports that Apollo visited the Hyperboreans, a people of myth, once every 19 years. The cycle’s name, enneadecaeteris, comes from the word for nineteen.

• Antikythera: The 2nd century BC mechanism applied the cycle, which points to the calendar’s popularity.
• Easter: A 19-year cycle is still part of computing the date of Easter each year.
• Calendars: The cycle forms the basis of both the Greek and the Hebrew calendars.

The lunar year of ancient Greek astronomy, 12 synodic months, runs about eleven days short. A gap of 22 to 33 days, a full month, opens every 2 to 3 years. Seven added months, one at a time, close that gap across the 19 years.

What role did the Attic calendar play in ancient Greek astronomy?

Ancient Greek astronomy connects with the Attic calendar, the lunisolar system of Athens and its territory, Attica. Lunisolar means it followed both the Moon and the solar year together. Its year opened at midsummer with the month called Hekatombaion.

Athenians lived by three calendars at once. A festival calendar had 12 months tied to the Moon and the solar year. A democratic state calendar ran on 10 arbitrary months. The star risings of ancient Greek astronomy fixed points in the agricultural calendar of seasons. No writer of the time described the whole system.

Ideally, ancient Greek astronomy placed the solstice near the end of Skirophorion, the final month. When the months had slid back far enough, roughly every three years, Athens repeated a month. The repeat produced a leap year of about 384 days. Poseideon, the sixth month, appears as the month repeated above all others.

The purpose of this calendar was fixing the days of religious festivals. Athenian months took their names from major festivals. Sumerian and Babylonian models named months after the main farm work. Maimakterion honoured Zeus Maimaktes, meaning Zeus the Stormy. The Great Dionysia, a leading city festival, gave no name to its month, Elaphebolion.

• Boeotia: Just across the border, the year began in midwinter and the months had different names.
• Delos: The island shared four of its twelve month names with Athens, in different places.
• Miletos: Four Athenian month names appeared here too, and Pyanepsion was the fourth month in both.

Each community judged its own new moon, with a degree of variation. Ancient Greek astronomy ties Meton and Euctemon to a nineteen-year cycle developed in Athens. No sign shows that Athens used it; its calendar appears to have run case by case.

What do the Pleiades add to ancient Greek astronomy?

Ancient Greek astronomy knew the Pleiades as a star cluster, and myth made them seven sister-nymphs. They served the hunting goddess Artemis as companions, and the stars were linked with rain. Their parents were the Titan Atlas and the Oceanid Pleione, a sea nymph.

In ancient Greek astronomy, the name reads as daughters of Pleione, yet the cluster’s name seems older. Another suggestion links it to plein, the Greek verb for sailing. Sailing in the Mediterranean opened with their heliacal rising, their first yearly appearance at dawn. The family story places the birth on Mount Cyllene.

Maia, the eldest, became the mother of Hermes by Zeus. Taygete bore Lacedaemon, also to Zeus. Alcyone bore Hyrieus by Poseidon, among other children. Merope, the youngest, married Sisyphus, became mortal and faded away. Her loss in myth seems to reflect a star of the cluster vanishing from naked-eye view.

After Atlas was made to carry the heavens, Orion began to pursue all seven sisters. Zeus turned them first into doves and then into stars, which comforted their father. The Orion constellation still chases them across the night in this story. Catasterism is the word for this turning of figures into stars in ancient Greek astronomy.

• Hesiod: The poem Works and Days repeatedly mentions them within the farming calendar.
• Sappho: One of her poems has the moon and the Pleiades gone at dead of night.
• Other version: A note on Theocritus makes them daughters of an Amazonian queen, credited with inventing ritual dances.

Hesiod describes the Pleiades setting in the west before dawn during October and November. Those months suited laying up a ship after the summer sailing. In ancient Greek astronomy, the same stars marked autumn, the Mediterranean time to plough and sow.

How did Aratus put ancient Greek astronomy into verse?

Ancient Greek astronomy reached a wide audience through the Phenomena, a poem by Aratus of Soli in Cilicia. Aratus was a didactic poet, meaning a poet who teaches. The first half sets a lost work by Eudoxus of Cnidus into verse.

Aratus studied with Menecrates in Ephesus and Philitas on Cos. In Athens he followed Praxiphanes, a philosopher of the school of Aristotle, and also met Zeno. About 276 BC the Macedonian king Antigonus II Gonatas invited him to court. There he wrote his famous poem on ancient Greek astronomy.

The Phenomena runs to 732 verses and introduces the constellations, with rules for their risings and settings. Northern groups are placed around Ursa Major, Ursa Minor, Draco and Cepheus. Orion serves as the starting point for the southern groups. The planets appear only as bodies with their own motion, and the poem gives no periods for them.

Its companion in ancient Greek astronomy, the Diosemeia or On Weather Signs, has 422 verses. It forecasts weather from signs in the sky and describes effects on animals. Its material comes largely from Aristotle, Theophrastus and Hesiod. Virgil later imitated parts of it in his Georgics. Nothing in either poem deals with Hellenistic astrology.

• Mirror: A second work by Eudoxus, the Enoptron or Mirror, also fed into the poem.
• Opening lines: The opening of the poem presents all things as dependent upon Zeus.
• Hipparchus: Hipparchus later compared the poem with his own observations and listed the differences.

Greek and Roman readers took up the poem widely, and commentaries and Latin translations survive. Historians of ancient Greek astronomy note its lack of precision, including wrongly drawn star groups. Aratus died at Pella in Macedon sometime before 240/239 BC.

Why does Orion the hunter matter to ancient Greek astronomy?

Ancient Greek astronomy knew Orion as a giant huntsman whom Zeus or Artemis set among the stars. Homer names him as a constellation in the Iliad, with the star Sirius as his dog. Hesiod uses his rising and setting to reckon the year.

In ancient Greece, Orion had a hero cult, a form of local worship, in Boeotia. Hyria, in the territory of Tanagra, is the birthplace named above all others. Tanagra still held a feast of Orion under the Roman Empire. The people there kept a tomb of Orion, seemingly at the foot of Mount Cerycius.

Hyginus gives three versions of how Orion entered the sky of ancient Greek astronomy. In one, Artemis and Leto ask Zeus to place him there after a scorpion kills him. Zeus agrees and adds the scorpion as well, as a memorial. In another, Orion chases Pleione for seven years until Zeus raises them all to the stars.

The same account of ancient Greek astronomy ties Orion to further star groups. Canis Major and Canis Minor are his dogs, and the one in front is called Procyon. They chase Lepus, the hare. Critics, says Hyginus, thought a hare too low a prey and gave him Taurus, the bull.

• Season: The constellation rises in November, when sailing ended, and people linked it with stormy weather.
• Sons: A papyrus fragment of Corinna, a poet of Boeotia, credits Orion with fifty sons.
• Art: The earliest clear image in classical art is Roman, from the Esquiline Hill, 50-40 BC.

The Odyssey shows Odysseus seeing him hunt in the underworld with a bronze club. Diodorus of Sicily, outside ancient Greek astronomy, has him build the headland forming Zancle’s harbour. Zancle is the old name for Messina in Sicily.

Which clock did the Tower of the Winds add to ancient Greek astronomy?

Ancient Greek astronomy left a timekeeping building in Athens, the Tower of the Winds. It is the only surviving clock tower from classical antiquity. Vitruvius and Varro name the astronomer Andronicus of Cyrrhus as its designer. It stands 12 metres tall.

A valve let water from the rear turret flow into the clock through a floor channel. Circular railings surrounded the central machine, set into hollows in the floor. People apparently walked around the clock and saw it from every side. Paper reconstructions of this machine of ancient Greek astronomy remain uncertain.

In ancient Greek astronomy terms, it possibly served as an astronomical clock showing a calendar and star groups. The Antikythera mechanism, found in a shipwreck, is a clock of that type. The original building had no windows. Its roof forms a smooth, shallow dome inside and possibly depicted the sky or served as a planetarium.

The height of the tower put its sundials and wind vane in view of the Agora. The Agora was the public square. Each sundial was customised to the hours of sunlight on its face. A further sundial sat on the turret at the back. The straight hour lines cut in the stone were once painted.

• Wind vane: Vitruvius describes a bronze sea god, Triton, on top, with a rod showing wind direction.
• Name: The Greek term horologion, from the word hora for hour, names a timekeeping building here.
• Designer: Little is known of Andronicus, not even whether he came from Macedonia or the Euphrates.

An alternative view credits this monument of ancient Greek astronomy to Attalus III of Pergamon. He died in 131 BC. It lay buried up to half its height under Ottoman rule. James Stuart and Nicholas Revett surveyed and drew it on an expedition in 1751-54.

What idea did Heraclides Ponticus bring to ancient Greek astronomy?

Ancient Greek astronomy owes a daily turning Earth to Heraclides Ponticus. He proposed that the Earth turns from west to east on its axis every 24 hours. Born in Heraclea Pontica, now Karadeniz Ereğli in Turkey, he migrated to Athens.

His father Euthyphron, a wealthy nobleman, sent him to study at the Academy in Athens. His teachers there were Plato and Speusippus. The Suda, a Byzantine encyclopedia, says Plato left him in charge on leaving for Sicily. That departure came in 361/360 BC. In 339/338 BC he narrowly lost the headship of the school to Xenocrates.

In ancient Greek astronomy, Heraclides held that a turning Earth creates the apparent daily motion of the stars. Hicetas and Ecphantus, both followers of Pythagoras, held the same view. It contradicted the model of Aristotle, in which the Earth stood fixed. Simplicius adds that he explained irregular planetary movements by moving the Earth and keeping the Sun still.

One account of ancient Greek astronomy gives him a system with the Sun circling the Earth. All other bodies in that scheme circle the Sun. Writers also praise him as the founder of the Sun-centred theory, but this is disputed. A detailed review of the sources finds no clear ancient reference to such support.

• Writings: All his writings are lost, and only fragments of them remain today.
• Range: He wrote on music, grammar, physics, rhetoric, history, mathematics and philosophy, at times in dialogue form.
• Nickname: A pun on his name, Pompicus, suggests that others mocked him as pompous.

Diogenes Laërtius reports that Heraclides wrote forged plays and credited them to Thespis. Dionysius the Deserter also fooled him with a forged play credited to Sophocles. His interest in ancient Greek astronomy sat beside a study of trances, visions and prophecies.

What did Pytheas of Massalia add to ancient Greek astronomy?

Ancient Greek astronomy reached the far north through Pytheas, an explorer and astronomer from Massalia. That Greek settlement stood on the site of modern Marseille in France. Around 325 BC he sailed out on a journey of discovery to Northern Europe.

His report of the voyage has vanished, so ancient Greek astronomy knows him through quotations in later writers. Scholars agree on one lost work, On the Ocean, built on a periplus. A periplus is a kind of written sailing record. Strabo and Pliny supply the largest share of the surviving passages.

In ancient Greek astronomy, a gnomon was a vertical rod that casts a shadow. At midday on the summer solstice at Massalia, Pytheas measured the height of the Sun. His rod measured 120 units, and the shadow came to one fifth less than 42. A modern check falls only 5 minutes of arc from the city’s true latitude.

Pytheas reported the north pole as an empty space at one corner of a four-sided figure. Stars marked the remaining sides, and calculations point to two in Draco and one in Ursa Minor. Polaris did not mark the pole then, because of precession, a slow shift in Earth’s axis.

• Thule: Ancient writers placed this island six days’ sail north of Britain, close to a frozen sea.
• Midnight sun: Pytheas is the earliest person on record to write about this northern summer sight.
• Tides: His account is the earliest known one that links the rise and fall of tides to the Moon.

Later ancient Greek astronomy still leaned on his numbers. Hipparchus accepted his shadow ratio and set Byzantium on the same parallel as Massalia. No earlier Greek scientist on record saw and described the Arctic and its polar ice.

Why do Philolaus and his Central Fire matter to ancient Greek astronomy?

Ancient Greek astronomy moved Earth away from the middle of the cosmos with Philolaus. He was a Pythagorean thinker from a Greek settlement in southern Italy. He pictured a Central Fire at the heart of the universe, with the Sun among the circling spheres.

Philolaus lived from about 470 to about 385 BC. Croton is the strongest candidate for his birthplace, though reports also name Tarentum and Metapontum. He moved to Greece, possibly after a Pythagorean meeting-place burned around 454 BC. Plato’s Phaedo names him as the teacher of Simmias and Cebes at Thebes.

In one surviving passage on ancient Greek astronomy, ten divine bodies dance around a fire at the centre. They are the sky, the five planets, the Sun, the Moon, Earth and a Counter-Earth. Aristotle reports that Philolaus added the unseen Counter-Earth because Pythagorean number theory required a tenth body.

Ancient Greek astronomy owes Philolaus a set of names for the layers of the cosmos. The highest region, where the elements stayed pure, was Olympus. The zone holding the five planets, the Sun and the Moon was the world. The part below the Moon and around Earth, the home of birth and change, was the sky.

• Book: Ancient reports credit him with the first published account of Pythagorean teachings.
• Fragments: Modern scholars accept about 11 fragments as genuine, all from his work On Nature.
• Harmony: He taught that limiting and limitless things join together in a harmony to form nature.

Copernicus named Philolaus nearly two thousand years later, in De revolutionibus. He wrote that Philolaus knew of Earth’s movement around a central fire. Histories of ancient Greek astronomy credit him with early ideas behind heliocentrism, a cosmos centred on the Sun.

Which battle links the eclipse of Thales to ancient Greek astronomy?

Ancient Greek astronomy has an early legend in the eclipse of Thales, a darkening of the Sun. Herodotus says the philosopher Thales of Miletus foretold it. If that account holds, no earlier eclipse on record was known before it happened.

Herodotus sets this ancient Greek astronomy story in Anatolia, now Turkey, during a conflict of Lydians against Medes. In the sixth year of fighting, day suddenly turned to night during a battle. Both armies stopped and began talks on peace. Later writers sometimes call this clash the Battle of the Eclipse.

The peace deal had two parts. Aryenis, daughter of the Lydian king Alyattes, married Astyages, son of the Median king Cyaxares. The Halys River, now the Kızılırmak, became the border between the kingdoms. Modern calculations tie the solar eclipse to the 28th day of the fifth month of 585 BC.

Ancient Greek astronomy at that date had no explanation for eclipses. The Moon’s role came to light over a century later, through Anaxagoras or Empedocles. One theory says Thales spotted patterns in eclipses, possibly the Saros cycle, a repeating series of eclipses. Babylonian skills of the time fell short of forecasting local conditions.

• Xenophanes: This thinker from the same century as Thales was impressed by the forecast.
• Cicero: Writing in the 1st century BC, he called Thales the first man to forecast a solar eclipse.
• Isaac Asimov: He called the battle the earliest event dated to the day, and the prediction the birth of science.

Modern scholars remain sceptical of the whole story. Histories of ancient Greek astronomy record no cycle at that time for forecasting a single location. A correct forecast rested on luck. One rival reading proposes a lunar eclipse at dusk, in 609 BC or 587 BC.

How did Callippus of Cyzicus refine ancient Greek astronomy?

Ancient Greek astronomy grew more detailed under Callippus, a mathematician and sky observer from Cyzicus. Born around 370 BC, he trained with Eudoxus of Cnidus at the school of Plato. He later worked beside Aristotle at the Lyceum in Athens.

Eudoxus had explained planetary movement through a scheme of connected spheres. Callippus watched the planets closely and judged the 27 spheres of that scheme not enough. He raised the count by seven to 34. The Sun and Moon gained two each, while Mercury, Venus and Mars gained one each. Aristotle’s Metaphysics preserves the description of those additions.

Ancient Greek astronomy also owes him careful measurements of the seasons. Starting from the spring equinox, he found lengths of 94, 92, 89 and 90 days. An equinox is a date of equal day and night. Those unequal seasons imply a change in the Sun’s speed, called the solar anomaly.

In ancient Greek astronomy, he followed Meton of Athens on the year and the lunisolar calendar. Lunisolar means a calendar that tracks both the Moon and the Sun. His own Callippic cycle runs across 4 Metonic cycles, a span of 76 years. His observations began at the summer solstice of 330 BC.

• Antikythera mechanism: This ancient mechanical clock from the sea off Greece carries a dial for his cycle.
• Manual text: The Greek wording of that device’s manual refers to the span of 76 years.
• Moon crater: A crater on the Moon bears the name Calippus in his honour.

Later ancient Greek astronomy used his starting point, with its star position, to check fresh observations. His Lyceum years place him in the city of Athens before the death of Aristotle in 322 BC. Callippus himself lived until about 300 BC.

What textbook did Cleomedes leave for ancient Greek astronomy?

Ancient Greek astronomy survives in part thanks to Cleomedes, a Greek writer of a basic textbook. The two volumes carry the title On the Circular Motions of the Celestial Bodies. Its shorter Latin title is Caelestia, which means The Heavens.

No record gives the birth or death dates of Cleomedes. Historians date his writing from the mid-1st century BC up to 400 AD. He cites Posidonius of Rhodes heavily, yet seems to pass over Ptolemy. The mathematician Otto Neugebauer studied his sky observations and settled on 371 AD, give or take 50 years.

His pages hold long passages of Posidonius, apparently word for word. None of the books by Posidonius reached the modern day, so ancient Greek astronomy values this copy. Cleomedes is also the original source for the famous tale of Eratosthenes measuring the distance around Earth. Modern mathematicians and astronomers find that description reasonable.

Cleomedes read the shadow on the Moon during lunar eclipses as a sign of a round Earth. He proposed that plenty of stars exceed the Sun in size. Seen from the surface of the Sun, he added, Earth resembles a tiny star. He also spent long passages attacking the science of the Epicureans, a school of philosophers.

• Moon illusion: He gave the earliest clear explanation for the Sun or Moon looking larger near the horizon.
• Refraction: He noted that light rays bend when passing from thinner into denser material.
• Moon crater: A crater in the northeastern part of the visible Moon carries his name.

Cleomedes used atmospheric refraction, the bending of light by air, to explain a sight in ancient Greek astronomy. The Sun and its rainbow, he suggested, stay visible when the Sun lies below the horizon. Ancient Greek astronomy counts him as a disciple of Posidonius.

Where does the Farnese Atlas fit into ancient Greek astronomy?

Ancient Greek astronomy takes solid form in the Farnese Atlas, a Roman marble of the 2nd century CE. It shows the Titan Atlas bearing a sky globe. No older known picture of the celestial sphere and the old constellations exists.

The statue dates to around 150 CE, and it appears to copy an earlier Hellenistic work. Hellenistic describes the age of Greek culture that followed Alexander the Great. Myth says Zeus sentenced Atlas to hold up the sky, so he strains under the weight. The figure stands 2.1 metres tall, and the globe measures 65 centimetres across.

For ancient Greek astronomy, the globe shows the night sky from beyond the last celestial sphere. That sphere is an imagined shell of stars. Low reliefs, meaning slightly raised carvings, mark 41 of the 48 Greek constellations listed by Ptolemy. Another count gives 42. Among them are the ram Aries, the swan Cygnus and the hero Hercules.

In 2005 the physicist Bradley Schaefer linked the globe to the lost star catalogue of Hipparchus. He argued that its constellations sit where they stood around 129 BCE. Critics, including Dennis Duke, strongly contest this view. The globe contains no actual stars, so ancient Greek astronomy gains no firm date from it.

• Naples: The National Archaeological Museum in this Italian city now holds the statue.
• Cardinal Farnese: Cardinal Alessandro Farnese acquired the figure in 1562, which gave it the present name.
• Villa Farnese: The sculpture went on show at this villa after the cardinal acquired it.

Among surviving statues of Atlas in ancient Greek astronomy and art, this one is the oldest. Atlas, a Titan of Greek mythology, appears earlier in Greek vase painting. Scholars have long presumed that the globe draws on star groups mapped in Hellenistic times.

Which star myths did the Catasterismi gather for ancient Greek astronomy?

Ancient Greek astronomy and star legend meet in the Catasterismi, a lost collection by Eratosthenes of Cyrene. Its Greek title means Constellations, or Placings Among the Stars. The book set out origin stories for the stars and the star groups.

For ancient Greek astronomy, the original text has not survived. Only a summary remains, the Epitome Catasterismorum. An epitome is a shortened version of a longer book. Its unknown writer sometimes goes by the label Pseudo-Eratosthenes, where pseudo means false. The summary comes from the 1st century BCE or CE.

The Epitome records how ancient Greek astronomy borrowed slowly from elsewhere. Greeks took over a zodiac from Mesopotamia, which reached them through Persian interpreters. A zodiac is a band of star groups along the path of the Sun. Greek myth then named single stars, clusters such as the Pleiades and Hyades, and whole constellations.

Chapters 1 to 42 of the Epitome treat 43 of the 48 constellations known to Ptolemy. The last chapters, 43 and 44, cover the five planets and the Milky Way. Five constellations go unmentioned: Corona Australis, Equuleus, Libra, Lupus and Serpens. Modern astronomers split its Argo Navis into Carina, Puppis and Vela.

• Hesiod: The Epitome cites a lost book called Astronomia, which bears the name of this ancient author.
• Hyginus: This writer produced the sole other ancient collection of star-placing stories, and it drew more attention.
• Venice: Erhard Ratdolt printed the first illustrated edition in this Italian city in 1482.

Classical Greece kept the wandering stars, or planets, apart from the gods steering them, as Plato did. In the later Hellenistic age, ancient Greek astronomy joined each planet to its god. A Greek-French scholarly translation with commentary appeared in 2013.

Why did ancient Greek astronomy link the Hyades with rain?

Ancient Greek astronomy turned weather lore into star lore with the Hyades, sister nymphs who bring rain. Popular tradition read their name as the rain-makers. Zeus placed them as a star cluster in the head of Taurus, the bull.

Nymphs are minor goddesses of nature in Greek legend. Atlas fathered the Hyades with either Pleione or Aethra. One version names other parents, Hyas and Boeotia. They count as sisters to the Pleiades and the Hesperides. Early sources list three of them, while late ones reach fifteen. The sisters’ names also change from writer to writer.

The main story explains their rainy reputation. When their brother Hyas died in a hunting accident, the sisters wept with grief. Ancient Greek astronomy held that rain always came with the heliacal rising and setting of this cluster. Heliacal refers to a star first or last seen near dawn or dusk.

Beyond ancient Greek astronomy, the Hyades also teach the infant Dionysus in certain tellings. Writers equate them with the Nysiads, nymphs who cared for him. Other nurses linked to them include the Lamides, the Dodonides and the nymphs of Naxos. Late sources make the sisters subject to old age, until Dionysus asked Medea to restore their youth.

• Open cluster: This loose star group in Taurus, the nearest of its kind to Earth, bears their name.
• Tennyson: The poem Ulysses by Tennyson recalls the rainy Hyades vexing the dim sea.
• Word origin: The name popularly suggests rain, yet an alternative origin lies in a Greek word for swine.

Two extra figures joined the group in ancient Greek astronomy. Thyone and Prodice, daughters of Hyas by Aethra, were added to these stars. The Greeks also tied the cluster to two families, sisters of Hyas and daughters of the ocean.

How did the bear myth of Callisto enter ancient Greek astronomy?

Ancient Greek astronomy explained the Great Bear through Callisto, whose Greek name means the fairest. In the myth she is a mountain nymph of Arcadia or the daughter of King Lycaon. Zeus sets her among the stars as Ursa Major.

Within ancient Greek astronomy lore, Callisto follows Artemis, goddess of the hunt, until Zeus pursues her. Versions of the story differ on who turns her into a bear. Hera, wife of Zeus, does it in one account, and Artemis does it in others. Apollodorus gives the deed to Zeus, who wants to hide her from Hera.

In Ovid, her son Arcas nearly kills the bear while hunting, sixteen years later. Jupiter, the Roman Zeus, places mother and son in the sky as the two Bears. Juno, the Roman Hera, asks Tethys to keep them from her waters. This gives a poetic reason for circumpolar stars, which never set.

Ancient Greek astronomy called the constellation Arktos, the Bear, or Helice in another origin story. A lost work, the Hesiodic Astronomia, names neighbouring Boötes as Arcas, the Bear-warden. All stars of Ursa Major stayed circumpolar over Athens in 400 BCE. Precession has since let the feet of the Bear dip below the Athens horizon.

• Phoenice: Eratosthenes mentions a variant where the nymph bears this name and becomes Ursa Minor.
• Athens shrine: Artemis Kalliste had a shrine outside the Dipylon gate, beside the road to the Academy.
• Modern names: An asteroid and the fourth Galilean moon around Jupiter both carry her name.

Julien d’Huy used statistical tools to link the tale with a Palaeolithic, or old Stone Age, myth. In ancient Greek astronomy stories, she stands as bear-mother of the Arcadians through Arcas. Ursa Major also tells Demeter to ask Helios about her lost daughter.

What did Greek city calendars take from ancient Greek astronomy?

Ancient Greek astronomy fed a patchwork of city calendars. Each Greek city-state ran its own year, built on the cycle of the Moon and religious festivals. Those years opened between autumn and winter in the great majority of states.

Ancient Greek astronomy in the age of Homer knew a year of twelve lunar months and 354 days. A lunar month follows one full cycle of the Moon. Each day of the month belonged to a chosen figure, such as the seventh day to Apollo. Scholars also counted time in Olympiads, the four-year span between Olympic Games.

Ancient Greek astronomy offered no shared calendar: month names and opening months differed between states. Certain places used no names and only counted the months. Numbered months spread in the second century BCE, possibly for uniformity across regions. Delphi matters greatly to modern reconstruction, since its records of freed slaves carry local dates and Delphian dates.

Evidence for the Rhodian calendar comes from a wealth of inscriptions. Rhodes inserted a 13th month, Panamos Embolimos, to bring lunar months back in step with the seasons. It fell after the 6th month and before the 7th, as a doubled Panamos. Scholars rate this calendar almost level with the Athenian one in depth of study.

• Boeotia: This region split its months into thirds, with three different ways to count the days.
• Elis: One view starts the Elian year at the winter solstice, though scholars dispute that reading.
• Thessaly: No single Thessalian calendar existed before 196 BC, when a common federal one followed.

Ancient Greek astronomy also reached machinery through these calendars. Month names from one Corinthian calendar run in order around the dial of the Antikythera mechanism. Thessaly’s federal year, in turn, split into two six-month periods for certain magistrates.

What do travellers ask about ancient Greek astronomy, and what are the answers?

The ancient Greek astronomy of Geminus, a writer of the 1st century BC, survives in a teaching book. His Introduction to the Phenomena was written for students. He also wrote on mathematics, though only quoted fragments of that work remain.

Which book did Geminus write on ancient Greek astronomy?

Geminus wrote the Isagoge, or Introduction, a beginners’ book drawn from astronomers such as Hipparchus. It covers the zodiac, the motion of the Sun, eclipses and phases of the Moon. It also calls weather forecasts from the stars foolish. References to mountains on Rhodes suggest that he worked there, though his birth there remains uncertain.

What placed Cassiopeia in the sky of ancient Greek astronomy?

Queen Cassiopeia of Aethiopia claimed more beauty than the Nereids, sea nymphs, and so angered Poseidon. An oracle of Zeus then demanded her daughter Andromeda as a sacrifice. Perseus killed the sea monster Cetus and saved Andromeda. Poseidon placed Cassiopeia in the heavens, chained to a throne that the constellation resembles.

Which tide theory did Seleucus add to ancient Greek astronomy?

Seleucus of Seleucia, born about 190 BC, backed the Sun-centred system of Aristarchus of Samos. Plutarch says he first demonstrated it through reasoning. Strabo credits him as the first to tie tides to the attraction of the Moon. He noted that tides varied in time and strength across the world.

Which role did Sosigenes play in ancient Greek astronomy?

Pliny the Elder records that Julius Caesar consulted Sosigenes while designing the Julian calendar. The reform arrived in 46 BC, a year of 445 days in Rome. That long year corrected errors in the old Roman calendar. Pliny also links Sosigenes to work on Mercury, which stays within 22 degrees of the Sun.