Ancient Astronomy



1700 BC

The king Hammurapi takes power in Babylon and early astronomy prospers, predating the beginnings of Greek astronomy.

A Dark Age in Greece

1100 BC

Ancient Greece loses its recently gained literacy, resulting in a dark age during which cultural development and scientific learning and practice decline until literacy returns around the 7th century BC.

Homer's Illaid and Odyssey

800 BC

Homer's two epic poems are the oldest pieces of Greek literature that remain to this day. To the humanities, these poems are the roots of a great deal of literary and artistic tradition. However it is interesting to note how the description of Achille's shield in the Illiad exemplifies the significance of astronomy in Greek culture as well as a knowledge of the stars.


700 BC

One of the earliest examples of astronomical practice is the MUL.APIN. This carved guide to the stars was intended to aid in farming in ancient Babylon.

Hesiod's Works and Days

650 BC

The work of the poet Hesiod remains one of the oldest pieces of Greek literature to date. The poem contains useful information regarding celestial risings and settings which were intended to help farmers and citiizens reckon time and tend their crops.

The First Spherical Model

500 BC

According to Roman intellectual, Sulpicius Gallus, Thales of Miletus was the first Greek scientist to represent the heavens with a sphere-shaped model. There is no way of knowing if this was a proper armillary sphere, as there is no confirmation of the model including an axis.


480 BC

The Greek astronomer moves to Athens to work under the support of Pericles. There, he develops explanations of both lunar phases and eclipses.

Aristotle and On the Heaven

470 BC

Aristotle forever changes science with one of his greatest works, on the heaven, which is his explanation of the nature of the heavenly sphere. The book explains the spherical shape of the earth, the composition of the various spheres of the cosmos, as well as information on the motions of the phenomena.

Herodotus and Gnomonics

450 BC

In his Histories, the Greek writer Herodotus confirms that the Greeks learned gnomonics from the Babylonians.

The Luni-Solar Theory

432 BC

The astronomer Meton of Athens proposes a nineteen year cycle of the sun and moon. This becomes the accepted luni-solar theory of Greek astronomy


400 BC

The ancients of Greece and Babylon record the risings and settings of stars on parapegma to help them reckon the time of the year.

Autocylus of Pitane

360 BC

Autocylus' On the Moving Sphere and On Risings and Settings are the oldest surviving works of Greek mathematical astronomy.

Alexander's Peak

331 BC

Alexander the Great Conquers Persia and gains more direct access to their scientific knowledge.

The Death of Alexander

323 BC

Alexander the Great dies of fever and his empire splits. His general, Ptolemaios I establishes a Greek-speaking dynasty in Egypt. Astronomical research does well in this kingdom, particularly at Alexandria


300 BC

The Babylonian astronomer's work survived as fragments inherited by Greek and Roman writers. He is attributed with an initial theory and description of lunar phases.

Timocharis and Aristyllos

290 BC

Timocharis and Aristyllos take the some of the earliest surviving measurements of the positions and motions of heavenly bodies. Their work helps later astronomers deduce such facts as the precession rate.


276 BC

Eratosthenes was a great intellectual of his day and his crowning work is his Geography. The work introduces geometrical methods to geography and uses gnomonics to generate one of the earliest measurements of Earth's size.

Aratus' Phaenomena

270 BC

The poet Aratus composes a poem that explains the arrangement and qualities of the constellations. The poem also gives weather signs, some of which are in relation to the movements of the stars.

Aristarchus of Samos

200 BC

Aristarchus is creditted with two major achievments: in his On the Sizes and Distances of the Sun and the Moon, he geometrically determines the distances between and dimensions of the sun, moon and earth. Furthermore he also discovered the Earth's dual motion, meaning Earth's simultaneous revolution about the sun and rotation about its axis.

Hypsicles of Alexandria

120 BC

Hypsicles work gives historians insights into the trigonometry of Greece during its astronomical peak. His book, Anaphorikos/Rising Times, shows how trigonometry is used to generate a table of ascensions.

Planetary Theory

100 BC

The first planetary theory originates in Babylon and is eventually adopted by Greece.

A Solar Theory

100 BC

A theory of the motion of the sun, which explains the irregularity of the seasons and the uniform circulation motion of the sun, emerges and is attributed to Hipparchus (this is mostly speculation due to lack of historical evidence on early solar theory).


100 BC

Hipparchus discovers the phenomena of precession. While he does not measure it accurately, he does prove that the stars are shifting along the ecliptic very slowly with the passage of time.

Julius Caesar

63 BC

Julius Caesar is elected Emperor an takes absolute power during his reign. He institutes the Julian calendar but is famously betrayed and killed in the Senate by those dissatisfied with his rule.

Vitruvius and his Books on Architecture

50 BC

Marcus Vitruvius Pollio writes his X Books on Architecture. Within he describes the necessity of gnomonics in architecture and includes an analemma for constructing sun dials.

The Julian Calendar

45 BC

Julius Caesar introduces the Julian calendar which persists for 100's of years despite inaccuracies in its time reckoning. It changes throughout its use, reaching a final form in 8 AD and is reformed by Pope Gregory in the 1500s.

Geminus; Introduction to the Phenomena

50 AD

Geminus, one of the later Greek astronomers, wrote an elementary textbook called an Introduction to the Phenomena. It contains good, general information about the practice of astronomy and was often used for introductory instruction.


100 AD

Like Geminus, Cleomedes also wrote an introductory book on astronomy. He entitled it On the Elementary Theory of the Heavenly Bodies. He references the work of Posidonius and Eratosthenes and generally presents the work in the frame of Aristotelian physics.


100 AD

Marinus is attributed by Ptolemy as having been one of the first scientists to use longitudes and latitudes in his work. He did not use them as extensively as Ptolemy in his analysis of the Phenomena

A Study of Precession

138 AD

Ptolemy's work in the Almagest brings the measurements of earlier astronomers such as Hipparchus and Timoachris in order to yield a precession rate. His answer is that the stars shift 1 degree every 100 years, but in reality the rate is 1 degree every 72 years. Ptolemy's rate goes uncorrected for centuries

The Almagest

138 AD

Ptolemy forever revolutionizes astronomy with his Almagest, a comprehensive guide to the motions and aspects of the heavens according to mostly Aristotelian physics. This becomes the go-to astronomical text for hundreds of years after antiquity and is still esteemed today

Theon of Alexandria

300 AD

Despite the astrolabe having been in use for many years, Theon writes history's first definitive treatise on the astrolabe. It does not survive today but is referenced in later works.

A Christian Rome

313 AD

The emperor Constantine, inspired by a vision before a battle, pledges to convert the empire to the teachings of Christ if he won. When he did, Rome became a Christian nation. However, many disbelieve in the vision story and consider the transition to a new religion to be politically motivated

Trepidation of the Equinoxes

800 AD

In order to account for precession and a noticeable decrease in the obliquity of the ecliptic over time, the Arab astronomer Thabit ibn Qurra proposes the theory of trepidation. The theory basically states that as time passes the ecliptic actually wobbles back and forth during its annual motions. it is accepted until refuted by Tycho Brahe.

Al Ma'mun and the House of Wisdom

813 AD

Al Ma'mun takes power in the new city of Baghdad. He establishes a multicultural confluence of scientists called the House of Wisdom. This institution makes Islamic astronomy the dominant form of astronomy in the middle ages.

The Alfonsine Tables

1270 AD

Commissioned by the King Alfonso X of what is now Spain, these tables were some of the most popular and disseminated tables of obliquity in the medieval astronomical tradition.

Chaucer on the Astrolabe

1300 AD

The oldest, surviving, English scientific work surfaces in the form of a Treatise on the Astrolabe. The famous Chaucer wrote it for his ten year old son, Lewis.

Georg Hartmann


Georg Hartmann is born and grows up to be one of the most celebrated astrolabe makers of the Renaissance. Aside from making fine ones for royalty, he also made cheap astrolabe kits for people of lesser means.


1543 AD

Copernicus releases a work entitled On the Revolutions of the Heavenly Spheres. This proposes a heliocentric model of the universe and causes a comparable amount of controversy to Darwin's Origin of Species

Tycho Brahe

1570 AD

Starting in the mid-1570's, Tycho Brahe and his apprentices study the heavens at his estate of Uraniborg. Most notably, they correct the precession rate which had been overestimated by the ancients.

The Gregorian Reform

October 4, 1582 AD

The Catholic church under Poper Gregory XIII institutes a permanent reform to correct the Julian Calendar. Do to inconsistencies between the Julian year and the tropical year, the calendar had fallen behind. The day after the reform, rather than being Oct 5th, was Oct 14th. The Gregorian reform also excluded certain leap years, like 1900, which are referred to as common years.

Kepler and the Ellipse

1609 AD

Johannes Kepler sends the practice of astronomy forward by explains the true nature of orbit in space. Rather than the heavenly bodies moving in circles, Kepler proves that orbital paths are elliptical

Isaac Newton

December 25, 1642

Isaac Newton is born and during his career completely revolutionizes physics. Among his astronomical achievements are the discovered the laws of universal gravitation and explains the nature of the heavens as a void of empty space inhabited by a swarm of planets, stars and other such bodies.