Ancient Greeks: Early Astronomy

Question 1

How old is the oldest record of astronomy (and what is it?)

Answer 1

Bone carving of the phases of the lunar cycle
Aurignacian culture of Europe
32000 BC

Question 2

Late Stone Age Europe

Answer 2

Goseck Henge, oldest solstice observatory
4900 BC
(That rock thing)

Question 3

Egypt

Also what other countries did stuff like this?

Answer 3

Pyramids and pole star
2600 BC
India, China, Mesoamerica, etc did stuff like this too

Question 4

Babylonians

Answer 4

Eclipse observations
Periodicity
Mathematics (base 60)
1200 BC

Question 5

Greeks (overview)

Answer 5

Realized sky is three-dimensional
Eudoxus’ concentric spheres model dominated cosmology for 2000y
400 BC

Question 6

Antikythera mechanism

Answer 6

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

Question 7

Greeks realizing sky is 3D

Answer 7

• 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

Question 8

Aristarchus

Answer 8

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?

Question 9

Eratosthenes

Answer 9

Calculated ABSOLUTE size of Earth
Given relative sizes (Aristarchus), can now compute absolute sizes
276-196 BC

Question 10

Hipparchus

Answer 10

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

Question 11

Angular size of sun and moon

Answer 11

1/2 degree

Question 12

Distance from syrene to Alexandria

Answer 12

5000 stades

1 stade maybe 185m?

Question 13

What are the two theoretical streams in astronomy at this time?

Answer 13

Philolaus - heliocentric (declined after Aristarchus)

Plato - geocentric (widespread acceptance after Ptolemy)

Question 14

Plato

Answer 14

428-348 BC
Asserted that all heavenly motions must be 
-in perfect circles
-at constant speed
(No evidence or physical explanation)

Question 15

Eudoxus

Answer 15

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

Question 16

Eudoxus’ model

Answer 16

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

Question 17

Problems with Eudoxus’ model

Answer 17

Does not explain changes in brightness of planets

Question 18

Apollonius

Answer 18

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

Question 19

Ptolemy

Answer 19

100-170 AD
He did detailed calculations and refined Apollonius’ model
Approximately correct!
Had an equal angle law ~ Kepler area law

Question 20

Ptolemy’s model

Answer 20

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)

Question 21

Almagest

Answer 21

Ptolemy
Compiled all existing Astro knowledge + own innovations
Dominated astronomy for 1500 years
Eventually overthrown by Copernicus, Galileo, Kepler, Newton

Question 22

What destroyed the Ptolemaic model?

Answer 22

Galileo’s observation of the phases of Venus

Question 23

Problems with the Ptolemaic model

Answer 23

Angular data can’t determine orbital radio of planets, can only find ratio of radii

Question 24

Define synodic period

Answer 24

Time between stuff appearing in sky in same configuration