Outline of Cosmology and Astronomy to Aristarchus

D. Joyce, Clark University

Source: Thomas Heath, Aristarchus of Samos, the Ancient Copernicus, Clarendon Press, Oxford, 1913. Reprinted by Dover, New York, 1981.


Thales of Miletus (c. 630? - c 550? BC) Statesman, engineer, mathematician and astronomer, one of the "seven wise men." Cosmology: earth floated on water, a disk. Sun, stars, and planets fiery. Perhaps based on Egyptian and/or Babylonian cosmology. Said to have predicted a solar eclipse, but unlikely. Eudemus referred to two written works by Thales On the Solstice and On the Equinox, since lost. Noted length of four seasons not all the same. Diogenes Laertius says Thales declared the apparent size of the sun and the moon to be 1/720 part of the circle described by it (i.e., 1/2 degree). Recommended sailing by Little Bear (Little Dipper) as the Phoenicians did.

Anaximander of Meletus (Anasimandros) (c. 611 - c. 547 BC) Considered first Greek philosopher. Student of Thales. Cosmology: earth at center, a disk with depth 1/3 of breadth floating in air. Believed the stars to be fiery wheels emitting flames through vents, and eclipses occur when the vents are stopped up. Concluded the circle of the sun is 27 or 28 times the size of the earth, and that of the moon 18 or 19 times. Probably brought the vertical sundial (gnomon) to Greeks from Babylonians. Said to be first to draw a map of the inhabited earth.

Anaximenes of Meletus (c. 585 - c. 528 BC. Stars on crystal sphere, but planets have their own movements. Sun, moon, stars made of fire. Said eclipses due to obscuring dark bodies.

Pythagoras of Samos (c. 580 - c. 500 BC). It seems Pythagoras believed the earth was a sphere as were sun, moon and stars, which he believed circled the earth.

Xenophanes of Colophon (c 570 - 478 BC). Poet, philosopher. Said lower side of earth reaches to infinity. Stars, sun, moon created and extinguished each day.

Heraclitus of Ephesus (fl. 504 BC). Heavenly bodies are bowls, insides are bright. Explains eclipses. New sun every day. Diameter of sun is 1 foot, same as its apparent size. 10800 years is total age of universe (30 times 360).

Parmenides (fl. 500 BC). Student of Xenophanes. Geocentric. Spherical earth as Pythagoras. Recognized Evening Star = Morning Star (Venus). Sun, moon, planets travel in "wreaths." Milky Way a wreath, too. Moon illuminated by sun.

Anaxagoras of Clazomenae (c. 499 - c. 427 BC) Believed sun lights moon & earth, and explained eclipses in terms of placement of sun, earth, and moon and other bodies. But said earth & heavenly bodies were flat or even concave. All circled earth.

Empedocles of Agrigentum (fl. 444 BC) Philosopher, politician, poet. Cosmology: stars on egg shaped crystal sphere. Inside crystal sphere is a sphere with a fiery light hemisphere, the other hemisphere dark, whose rotation brings day & night. The sun is a reflection on the crystal sphere of the light hemisphere! Believed light travels and takes time to pass from one point to another.

Oenopides of Chios (c. 450? BC) Discovered obliquity of ecliptic. Gave a great year as 59 years.

Leucippus of Elea (fl. 450 BC) and Democritus of Abdera (b. c. 460 BC), atomists. Leucippus: earth a disk; moon, circle of stars, and sun rotate around earth in that order. Democritus agreed more or less with Leucippus and Anaxagoras.

Philolaus of Croton (c. 390 BC) and later Pythagoreans. Cosmology: fire at center of universe, all else rotates around the central fire. All planets including earth are spheres. Order out from central fire: counterearth, earth, moon, sun, Venus, Mercury, Mars, Jupiter, Saturn, sphere of stars. Distances to central fire described as harmony of the spheres, ratios corresponding to different pitches, but actual ratios not recorded. Earth always faces away from central fire. Sun glassy, reflecting light from central fire or perhaps other sources. Moon receives light from sun explaining phases of moon. Eclipses of moon when earth or counterearth between sun and moon.

Plato (427 - 347 BC) Treated astronomy in the same Platonic way as he treated math -- as a problem to find uniform and ordered movements to account for apparent movements. Earth sphere; sun lights moon. Order from earth: moon, sun, Venus, Mercury, Mars, Jupiter, Saturn, sphere of stars.

Eudoxus of Cnidus (c. 408 - c. 355 BC) Learned Egyptian astronomy at Heliopolis and made observations there. Theory of concentric spheres (book lost) explained in Aristotle's writings. The sphere of stars rotates about earth; the sun's and moon's motions each compounded of three motions (rotating sphere concentric with the sphere of stars, traveling the circle of the zodiac, and traveling a smaller circle inclined to the zodiac; each planet compounded of four motions.

Callipus of Cyzicus (c. 370 - c. 300 BC) Added two more spheres to sun & moon, one to each planet, to account for variances such as differing lengths of seasons.

Aristotle (384 - 322 BC) Modified Callipus' theory by adding more spheres.

Heraclides of Pontus (c. 390 - c. 322 BC) Claimed earth at center of universe, but revolving about axis. Also claimed Mercury and Venus orbit the sun.

Aristarchus of Samos (c. 310 - 230 BC) In the extant On the Sizes and Distances of the Sun and Moon concluded the sun was 18 to 20 times as far from the earth as the moon, based on the observation that at half-moon, the angle between the sun and moon was 87 degrees (it's actually much closer to 89 degrees and 50 minutes). Developed heliocentric cosmology: earth orbits sun in circle and revolves on an inclined axis, planets orbit sun in circles, moon orbits earth in a circle.

Seleucus of Seleucia (c. 150 BC) Accepted Aristarchus' heliocentric theory (only one who did) and used it to explain connection between tides and moon.

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