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Aristarchus of Samos -                  c. 270 BC

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Aristarchus of Samos -                  c. 270 BC

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Proposed an alternate cosmology (arrangement of the universe): a heliocentric model of the Solar System, placing the Sun, not the Earth, at the center of the known universe. Also wrote On the Sizes and Distances of the Sun and Moon and used trigonometry to estimate the size of the Moon and its distance by the Earth's shadow during a lunar eclipse.

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Aristillus of Samos and Timocharis of Alexandria -             c. 300 BC

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Aristillus of Samos and Timocharis of Alexandria -             c. 300 BC

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Prepared the first true star catalogue (used later by Hipparchus to compare the recorded positions from his own measurements)

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Calculated the diameter of the earth by measuring noontime shadows at sites 800 km apart. Assuming the earth is a sphere, the measured angle between the sites is seven degrees and the circumference is about 50 times 800 km, or about 40,000 km.

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Introduced two new mechanisms that allowed a planet to vary its distance and speed: the eccentric deferent and the deferent and epicycle. Also probably first invented the terms 'parabola' and 'hyperbola,' curves formed when a plane intersects a conic section, and 'ellipse,' a closed curve formed when a plane intersects a cone.

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Wrote On the Ascension of Stars. In this work he is the first to divide the Zodiac into 360 parts.

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Built off existing Babylonian astronomical writings and used them to create better geometrical models of the sun and moon. Also measured the year with great accuracy and built the first comprehensive star chart with 850 stars and a luminosity, or brightness, scale. He is credited with the discovery of the precision of the equinoxes by Ptolemy.

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Designed a calendar of 365.25 days which was introduced by Julius Caesar. Also credited with developing models of the orbit of Mercury.

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Death of Alexander the Great, beginning of The Hellenistic Period.

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Seleucos conquers Babylon and founds the Seleucid dynasty.

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Life of Archimedes, physician, mathematician and engineer.

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Rome defeats the Celts in Italy. Rome's dominance in central Italy is secured.

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Eumenes rebels and wins against the Seleucid Antiochus I. Beginning of the Pergamon Empire.

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Former satrap Diodotos rebels against Seleucid king Antiochos I, creating the Greco-Bactrian kingdom.

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First appearance of multiple Euthydemid kings at the same time. Beginning of the Indo-Greek kingdoms.

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Rome sacks Corinth and dissolves the Achaean league. Greece is ruled by Rome

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Tigranes II invades and destroys the Seleucid Empire.

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Julius Caesar's conquest of Gaul.

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Herod the Great is installed as King of Judaea. Rebuilding of the Temple of Jerusalem.

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The death of Cleopatra VII by poison, the last ruler of Ptolemaic Egypt. The end of the Hellenistic period.

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Attalus III, the last king of Pergamon, bequeathes the whole of Pergamon to Rome.

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On his pursuit of Pompey into Egypt, Caesar was cut off by a large fleet of Egyptian boats in the harbor of Alexandria. He ordered the boats to be burned. The fleet was destroyed, but the flames spread to the city and the great library.