The Middle East: 249–238 BCE

Parthian Emergence and Hellenistic Decline

Rise of Arsaces and the Parthian State

In 247 BCE, following the death of Antiochus II, Seleucid control weakens as their governor (satrap) of Parthia, Andragoras, declares independence amidst the turmoil caused by the seizure of the Seleucid capital Antioch by Ptolemy III. Andragoras struggles to defend his territory without Seleucid military backing.

Around 238 BCE, the situation deteriorates further when Arsaces, a leader of the nomadic Parni tribes of Scythian or Bactrian origin, launches a decisive invasion into Parthia, aided by his brother Tiridates. Quickly capturing Astabene (Astawa) and its capital, Kabuchan (modern Kuchan), the Parni decisively end Andragoras' rule, killing him in the process. The Parni tribes subsequently adopt the name Parthians, derived from the conquered province, marking the birth of a new and influential Persian dynasty.

Advances in Hellenistic Astronomy

Amidst these geopolitical shifts, significant advancements occur in Greek astronomy. Aristarchus of Samos, a prominent student of Strato of Lampsacus, advocates for a revolutionary heliocentric model, asserting that the Sun, not the Earth, is the center of the universe. Aristarchus also conducts pioneering work in determining celestial distances. In his surviving treatise, On the Sizes and Distances of the Sun and Moon, he uses geometric reasoning to calculate that the Sun is approximately twenty times further away and twenty times larger than the Moon. Although his estimates are imprecise due to technological limitations, Aristarchus's methods remain conceptually sound and significantly influence future astronomical thought.

Aristarchus of Samos, a student of Strato of Lampsacus who flourishes in the mid-third century BCE, champions the notion of a Sun-centered universe and makes a pioneering attempt to determine the sizes and distances of the Sun and Moon.

Aristarchus’ only surviving work, On the Sizes and Distances of the Sun and Moon, details his remarkable geometric argument, based on observation, whereby he determined that the Sun is about twenty times as distant from the Earth as the Moon, and twenty times the Moon's size. (Both these estimates are an order of magnitude too small, but the error stems from Aristarchus' lack of accurate instruments rather than in his faultless method of reasoning. Scant evidence exists concerning the origin of his belief in a heliocentric world system; his theory, rejected by his contemporaries, is known only because of a summary statement in Archimedes' The Sand Reckoner.)