Ancient Greek Astronomy - Part 1

Introduction to Ancient Greek Astronomy

  • Overview of Ancient Greek Astronomy

  • Study period: ~3000 BCE to ~300 CE

Ancient Greek Context

  • Shift from astrology and religious motivations to a scientific approach

  • Fragmented geography and decentralized rule contributed to advancements in astronomy

Timeline of Ancient Greece

  • < 3000 BCE: Arrival of Greeks in Aegean Peninsula

  • ~750 BCE: Recorded history begins with the founding of Rome

  • ~750 - 480 BCE: Archaic Period: formation of city-states and expansion into new territories (Turkey, Spain, France, Italy, Russia, Africa)

  • 480 - 323 BCE: Classical Period: ends with the death of Alexander the Great

  • 323 - 156 BCE: Hellenistic Period: Cultural expansion into the Middle East and Egypt

  • 156 - 30 BCE: Greco-Roman Period: ends with the death of Cleopatra VII

Theories of the Cosmos

  • Geocentric Theory: Earth as the center of the universe

  • Heliocentric Theory: Sun as the center

  • Initial development of both theories but dominated by Geocentric due to Plato and Aristotle's influence

Philosophical Timeline of Ancient Greece

  • 600 BCE: Ionian Philosophers (Thales, Anaximander)

  • 500 BCE: Pythagorean Philosophers

  • 400 BCE: Plato, Eudoxus, Aristotle, Apollonius

  • 200 BCE: Hipparchus, Ptolemy

  • Contribution from notable Helio- and Geocentrists like Philolaus, Herakleides, Aristarchus.

Contribution of Ionian Philosophers

Thales and Anaximander

  • Thales of Miletus (c. 625 BCE)

    • Sought natural explanations for phenomena

    • Example: Proposed earthquakes resulted from Earth floating on water

Anaximander** (c. 610 BCE)

  • First cosmologist, provided initial ideas about the universe’s origins

  • Introduced the concept of testable models in cosmology

The Pythagoreans

  • Another influential group in Ancient Greek Astronomy

Pythagoras (c. 570 BCE)

  • Noted for the relationship between mathematics and nature

  • Concluded universal order through harmony and numbers

  • Formed a cult-like group focusing on mathematical laws and the worship of numbers

Key Pythagorean Beliefs

  1. Celestial bodies move in perfect circles

  2. The Earth is a perfect sphere

  3. Evidence for Earth's Shape:

    • Ships disappearing bottom-first on the horizon

    • Circular shadow of Earth during lunar eclipses

    • Constellations shifting when moving north/south

Heliocentrism's Early Models

Philolaus (c. 470 BCE)

  • First to suggest Earth’s motion, reducing complexity in celestial observations

  • Introduced the notion of the 'Central Fire' model, placing Earth in motion around it.

Herakleides (c. 390 BCE)

  • Proposed a daily spin for Earth to explain observable celestial phenomena

  • Suggested Venus and Mercury orbits around the Sun to explain their proximity and brightness.

Aristarchus (c. 310 BCE)

  • Authored 'On the sizes and distances of the Sun and Moon'

  • Developed methods for measuring the size and distance of celestial bodies

  • Attempted to place the Sun larger than the Earth, challenging the geocentric view.

Measurements by Aristarchus

  • Used Earth’s shadow on the Moon to determine relative sizes

  • Calculated angles between the Moon and Sun to formulate distance measurements

Conclusion of Aristarchus’ Work

  • Despite his early claims, Aristarchus’ heliocentric model fell into obscurity due to Aristotle's pervasive influence.