Astronomy Timeline – focus on Western Civilization

 

8^th c  BC, Ancient Greece – Homer mentions Pleiades, Orion, Taurus, Bootes, The Great Bear, and Sirius in his poetic works.

 

6^th c BC, Ancient Greece – Thales of Miletus predicts eclipses and determines length of year using zodiac signs.  Pythagoras proposes that the universe consists of nested spheres around Earth, with each planet on one sphere – friction between spheres caused “music of the spheres”.

 

4^th c BC, Ancient Greece – Among many other things, Aristotle correctly explains lunar phases and eclipses and shows Earth is spherical; he also advocates geocentric universe. 

 

3^rd c BC, Ancient Greece – Aristarchus of Samos proposes a Sun-centered universe, but fails to provide evidence; he also attempts to measure the distance from Earth to the Sun and the relative sizes of the Earth, Moon and Sun, using angular ratios.  Eratosthenes calculates the radius of the Earth using angular ratios and proves that Earth is a sphere.

 

2^nd c BC, Ancient Greece – Hipparchus of Rhodes compiles the first star catalog and devises the magnitude system to catalog brightness of stars; he also measures the distance to the Moon (29 ½ times the Earth’s diameter, correct value is 30) and discovers the Earth’s wobble, known as precession. 

 

125 AD, Ancient Greece - Claudius Ptolemy presents a math based description of the movements of the Sun, Moon, stars and planets in a geocentric system, and introduces epicycles to explain erratic motion of planets; he sticks to the concept of perfectly circular orbits. 

 

13^th  c AD – St. Thomas Aquinas incorporates Aristotle’s teachings and Ptolemy’s geocentric model into Christian thinking (“No conflict between faith and reason”). 

 

16^th c AD, Poland – Nicolaus Copernicus proposes a heliocentric (Sun-centered) model at the end of his work, De Revolutionibus, but model still needs refining as it includes perfect circular orbits (Ptolemy’s model is still more precise at this point, although much more complicated). In Denmark, Tycho Brahe witnesses a supernova in Cassiopeia in 1572 – in the “unchanging” heavens; he remains skeptical of the heliocentric model and develops a Tychonian model of the universe (Earth at Center, Sun and Moon revolve around Earth, but all other planets revolve around the Sun); he also collects 20 years of precise data of the nightly position of Mars.  Brahe hires Johannes Kepler (Germany) as an assistant.

 

17^th c AD – Kepler uses Brahe’s data to show that planetary orbits are elliptical, not circular.  In Italy, Galileo Galilei uses telescope in 1609 to see mountains on Moon, the four largest moons of Jupiter, Saturn’s odd shape, sunspots, the Sun’s rotation, the phases of Venus, and countless stars beyond naked eye view.  Galileo also performs scientific experiments and disproves Aristotle’s teachings of physics.  In England, Isaac Newton (arguably) invents calculus, discovers properties in optics, and develops a universal law of gravitation (written into his work, the Principia Matematica), and progresses the idea of a mechanical “clockwork” universe. 

 

 

20^th c AD – Albert Einstein publishes (1905) Special Theory of Relativity (nothing moves faster than light; you cannot separate space from time), and (1916) General Theory of Relativity (gravity is a warping of space and time; light paths can bend with gravity).  There is much more to come…