10000BC
calendar refinements for agriculture
counting schemes
months, year (in months, but uneven)
3000BC
# of days in year: ~360 (so 360 degrees in circle)
heliacal rise of Sirius in Egypt -> 365 days
celestial pole
modern constellations (from Med. sailors)
soltices, equinoxes, Astrology
astronomical monuments (Stonehenge, Pyramids, etc.)
astronomy strong in Mesopotamia/Europe, China, Africa,
Polynesia, Americas: everywhere!
500BC
Pythagorus - concentric celestial spheres for Sun, Moon, planets - all bodies spherical (including Earth)
Philolaus - Earth goes around central fire (Sun)
350BC
Aristotle - Sun is further than Moon (slower against stars), eclipses - Earth is round (shadow on Moon), going north makes pole star rise
- choose geocentric model: feels like it; no stellar parallax
300BC
Aristarchus - size of Sun and Moon relative to Earth, relative distances (use of geometry to deduce them)
- Sun is much bigger, so choose heliocentric model (doesn't take hold, Aristotle wins)
Eratosthenes - size of the (spherical) Earth is measured between Alexandria and Syene => R(earth)~7000km
using geometrical reasoning : D(sun)/D(moon)~20 , R(earth)/R(moon)~20 , R(sun)/R(earth)~7
150BC
Hipparchus - star catalog (850, position and brightness)
- better estimates of size and distance of Moon
R(earth)/R(moon)~8/3, D(moon)~60R(earth), D(sun) big
- precession of Earth's pole
-epicycles and deferent (used by Ptolmey) to explain retrograde motion of planets
150AD
Ptolmey - worked out a full geometric geocentric cosmology
- accounts for retrograde motion of planets
- predicts planetary positions
- 55 concentric cosmic spheres, all circular motion
(size of Universe about 20000R(earth))
Dark Ages
Europe stays with Aristotle and Ptolmey; Arabs
improve on that and make better catalogs and predictions (but the better
the observations got, the harder it was to make it work); Chinese keep
very careful astronomical records; Mayans work out very good calendar (which
just ended); everyone uses astronomy to do astrology (astronomers valued
as prognosticators)
1500AD
Copernicus - shows you could calculate planetary positions more elegantly and simply (but not more accurately), with uniform circular motions using Sun as center
- relative distances of planets from Sun (better periods)