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Astronomy
10, Spring 2000 |
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Historical Astronomy
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,
Polonesia,
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
Eratosthenes
- size of the (spherical) Earth is measured between Alexandria and Syene
R(earth)~7000km,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 EarthÕs 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)