Early Astronomy in the University of Michigan Collections

Ptolemy and Later Greek Astronomy

Page of a rare book (fragment)

The astronomical tradition of the Hellenistic and Roman period was collected and systematized by Claudius Ptolemaeus or Ptolemy (ca. 105-175 CE). He is the most prominent astronomer of antiquity and the one whose works have reached us most extensively. His Almagest (the name derives from the Arabic title al-Majisṭī, which in its turn derives from the Greek Megistē Syntaxis, “Greatest Collection”, itself a corruption of the original title, Mathēmatikē Syntaxis, “Mathematical Collection”) was published around 150 CE and became the foundation of western astronomy until Kepler. Ptolemy reorganized and reworked past theories, often improving on them through his own observations and calculations. In fact, Ptolemy could benefit from the mathematical work done by Menelaus in the 1st century CE (Ptolemy mentions two of his observations made in 98 CE). In his Spherics Menelaus studied the geometry of spherical triangles; even if his original work is lost (we only have translations in Arabic), it probably marked the beginning of spherical trigonometry, a new discipline which finally made it possible to carry out precise calculations on the celestial sphere. In particular, the so-called “Menelaus’ Theorem” was very much used by Ptolemy and by subsequent astronomers (many Islamic astronomers wrote works on it).

Ptolemy also organized the first scientific catalogue of stars (with ecliptic coordinates, for the year 137 CE), which is the basis of modern star catalogues; his model for solar and planetary motions (deferent-and-epicycle model with equant point) was so precise at predicting planetary and solar motions that later astronomers up to the time of Kepler mostly just modified it rather than proposing major changes. This included Copernicus who adapted many parts of Ptolemy’s theories and models to a heliocentric model. Ptolemy also wrote about astrology, in a work known as the Tetrabiblios, because during his time astrology and astronomy were closely connected and not considered incompatible as in modern science.

After Ptolemy Greek astronomy greatly slowed its progress; the works of later astronomers mostly consist of commentaries (for example, those of Pappus and Theon on Ptolemy’s works, dating to the fourth century CE) and collections of past achievements, mostly for school uses. The teaching was organized through the so-called Little Astronomy (a collection of the following works, considered preparatory to the studying of Ptolemy’s Almagest: Theodosius, Spherics; Autolycus, On the Moving Sphere; Euclid, Optics; Euclid, Phenomena; Theodosius, On Geographic Places; Theodosius, On Days and Nights; Aristarchus, The Sizes and Distances of the Sun and Moon; Autolycus, On Risings and Settings; Hypsicles, On Ascensions; Euclid, Catoptrics; Euclid, Data) and then the Almagest (or Syntaxis). In fact, the immense success of Ptolemy’s Syntaxis also caused the works of the previous astronomers such as Hipparchus to be forgotten. The other texts that survived and reached us directly were the easier texts such as Aratus’ Phaenomena or introductions to astronomy such as the ones written by Geminus (first century BCE) and Cleomedes (ca. 200 CE), aimed at amateurish readers or beginner students rather than at professionals.

Hellenistic Greek Astronomy

Babylonian and Greek Astronomy

Islamic Astronomy


Roman Empire

  • Battle of Actium: Octavian wins over Mark Antony and Cleopatra (31 BCE).
  • Egypt becomes a Roman province with a special status (30 BCE).
  • Octavian becomes the first Roman Emperor with the name of Augustus (27 BCE).
  • Augustan Age (literary authors: Virgil, Horace, Ovid; Livy) (30 BCE-14 CE).

25-20 BCE Cistophorus minted in Ephesus. KM 1991.02.0319

23/22 BCE Alexandrian Calendar.

12 BCE Denarius minted in Lugunum. KM 1991.02.0320

early 1st century CE Hyginus’ Astronomy.

Roman Empire

  • Julio-Claudian emperors: Tiberius, Caligula, Claudius, Nero (literary authors: Lucan; Seneca the Younger; Petronius) (14-68 CE).
  • Flavian emperors: Vespasian, Titus, and Domitian (literary authors: Elder Pliny; Martial; Quintilian) (70-96 CE).

16–17 CE Germanicus’ Aratea.

1st century CE Fragment of an anonymous treatise giving predictions, probably based on the conjunctions of the moon. P.Mich. III 148 = P.Mich. inv. 4.

1st century CE Dorotheus’ Carmen Astrologicum.

1st century CE Menelaus (observations in 98 CE).

Roman Empire

  • Maximum extension of the Roman Empire under Trajan (literary authors: Tacitus; Juvenal; the Younger Pliny) (98-117 CE).
  • Antoninus Pius (emperor: 138–161 CE).
  • Marcus Aurelius (emperor: 161–180 CE).

ca. 150 CE Claudius Ptolemy’s Almagest and Tetrabiblios.

2nd century CE Planetary Melothesia. P.Mich. III 149 = P.Mich. inv. 1.

Roman Empire

  • Severan emperors: Septimius Severus, Caracalla, Geta, Elagabalus, and Severus Alexander (193-235 CE).
  • Constitutio Antoniniana or Edict of Caracalla: all free men of the Empire are given Roman citizenship (212 CE).
  • ‘Third Century Crisis’ (235-284 CE).

ca. 200 CE Cleomedes’ Meteōra.

3rd century CE Astronomical table for the calculation of the longitudes of the planet Mars. P. Mich. III 151 = P. Mich. inv. 924.

Roman Empire

  • Probus (emperor: 276–282 CE).
  • Diocletian (emperor: east, 284–305 CE).
  • Diocletian divides the Empire into two regions, east and west (286 CE).
  • Constantine I (emperor: 306–337 CE).
  • Constantine’s Edict of Milan grants religious liberty to Christianity and all other religions (313 CE).
  • Constantine moves the capital of the Empire from Rome to Byzantium (324 CE, renamed Constantinople in 330 CE).

279 CE; 304 CE Horoscopes for two births. P.Mich.inv. 6664.

ca. 300–320 CE Pappus’ Commentary on Ptolemy’s Almagest.

334/335 CE? Fragmentary list of full moons, giving hours and longitudes. Mich. III 150 = P. Mich. inv. 3823.

Roman Empire

  • Constantius II (emperor: 337–361 CE)

360 CE Avienus’ Aratea.

Roman Empire

  • Theodosius I (emperor: east, 379–392 CE; east and west, 392–395 CE).
  • Theodosius I makes Christianity the official religion of the Roman Empire (380 CE).
  • Theodosius I bans the Olympic Games (393 CE).
  • at the death if Theodosius I, the Roman Empire definitely separates between the Western Empire (capital Rome) and the Eastern Empire (capital Constantinople) (395 CE).

ca. 360-380 CE Theon’s work on Ptolemy (Commentary on Ptolemy’s Almagest, edition of and two commentaries on Ptolemy’s Handy Tables).

Roman Empire

  • Anthemius (emperor: west, 467–472 CE).
  • Leo I (emperor: east, 457–474 CE).
  • Fall of the Western Roman Empire (476 CE).

467 CE Astronomical Ephemeris for 467 CE. P.Mich.inv. 1454 recto.