Ancient Greeks: Early Astronomy Flashcards
How old is the oldest record of astronomy (and what is it?)
Bone carving of the phases of the lunar cycle
Aurignacian culture of Europe
32000 BC
Late Stone Age Europe
Goseck Henge, oldest solstice observatory
4900 BC
(That rock thing)
Egypt
Also what other countries did stuff like this?
Pyramids and pole star
2600 BC
India, China, Mesoamerica, etc did stuff like this too
Babylonians
Eclipse observations
Periodicity
Mathematics (base 60)
1200 BC
Greeks (overview)
Realized sky is three-dimensional
Eudoxus’ concentric spheres model dominated cosmology for 2000y
400 BC
Antikythera mechanism
100 BC Archimedes? Hipparchus? Who knows Super super cool All these super precise gears predicted all this stuff "More valuable than Mona Lisa" Like 2000 years ahead of its time
Greeks realizing sky is 3D
- immediately explains phases of moon
- explains eclipses
- what is SHAPE of earth? (Pythagoras, Aristotle)
- what is SIZE of earth compared to moon?
- can use lunar eclipses to see shape
Aristarchus
310-230 BC
Calculated RELATIVE distances (ex earth to sun/earth to moon ratio)
Calculated RELATIVE sizes (ex diameter of sun/diameter of moon ratio)
Did this inspire his unprecedented belief that Earth orbits the Sun?
Eratosthenes
Calculated ABSOLUTE size of Earth
Given relative sizes (Aristarchus), can now compute absolute sizes
276-196 BC
Hipparchus
190-120 BC
Accurately catalogues 100s of star positions
Discovered precession of equinoxes
Determined length of year to within 6 min
Established stellar magnitude scale
Computed more accurate EM distance
Now more absolute distances can be found
Angular size of sun and moon
1/2 degree
Distance from syrene to Alexandria
5000 stades
1 stade maybe 185m?
What are the two theoretical streams in astronomy at this time?
Philolaus - heliocentric (declined after Aristarchus)
Plato - geocentric (widespread acceptance after Ptolemy)
Plato
428-348 BC Asserted that all heavenly motions must be -in perfect circles -at constant speed (No evidence or physical explanation)
Eudoxus
400-347 BC
- Student of Plato
- First to attempt mathematical explanation of celestial motions (apparent circular motion of stars, apparent retrograde motion of Mars)
- complexities with planetary motion: retrograde and changing brightness
Eudoxus’ model
Rotating sphere of stars Rotating sphere of ecliptic inside First sphere inside for synodic period Second sphere inside for synodic period Earth at centre Nested spheres, inner sphere axis offset, planet in equator Outer sphere CCW, inner sphere CW
Problems with Eudoxus’ model
Does not explain changes in brightness of planets
Apollonius
240-190BC Introduced circle upon circle at constant speeds to explain varying speed and distance of moon and sun Looks ~ pretty close to orbit He was circle crazy Hipparchus backed him up with math
Ptolemy
100-170 AD
He did detailed calculations and refined Apollonius’ model
Approximately correct!
Had an equal angle law ~ Kepler area law
Ptolemy’s model
Apollonius, but added
Eccentric (equivalent to a certain type of epicycle) (earth not centre of circle)
Equant (constant angular speed from Equant, varying physical speed along deferent) (sacrilege) (earth is off centre)
Almagest
Ptolemy
Compiled all existing Astro knowledge + own innovations
Dominated astronomy for 1500 years
Eventually overthrown by Copernicus, Galileo, Kepler, Newton
What destroyed the Ptolemaic model?
Galileo’s observation of the phases of Venus
Problems with the Ptolemaic model
Angular data can’t determine orbital radio of planets, can only find ratio of radii
Define synodic period
Time between stuff appearing in sky in same configuration
