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Astronomy Rough Notes - Copernican Revolution
BRING:
Powerpoint
Software for sky
Geocentric model
Heliocentric model
Earth globe
HANDOUTS:
None
QUICK OVERVIEW
What is science?
Pre-Copernican Astronomy
Next time - Copernican Revolution
SCIENCE:
Science - A process of knowing
Differs from theology or philosophy
Way to get passed the conflicts in various belief systems (by looking at evidence)
Sagan: “It doesn’t matter if it makes you feel good. What matters is, is it true?”
Observe
Question
Model (hypothesize)
Predict
Test
Revise
You use the process all the time in daily life
Examples: Car stops….
Flashlight doesn’t work…
Cooking…
Hallmarks of science (How science stands apart. See Bennett - Cosmic Perspective )
Uses natural explanations (not supernatural)
Uses models that make testable predictions
K.I.S.S. (Occam’s Razor)
Theory vs. Law
Theory is stronger than Law in normal science terminology
Law - What happens
Predicts what will happen in specific cases
Ex - Universal Law of Gravity
If you drop a rock, it will fall down (and what force is exerted on it)
Theory - Explains why things happen
Includes laws
Allows predictions of new tests of itself
Ex - General Theory of Relativity
Explains WHY gravity works
Includes the Law of Gravity BUT ALSO more
Explains the precession of Mercury’s perihelion
Predicts the existence of Black Holes
Supported by many scientists
Supported by many testable predictions
Can never can be proven but has not been disproven
These can always be modified, based on new data/information
Exercise: Science or Not Science and why not
Can you investigate these using science?
If so, does science support the idea?
If not, why not?
1. A car can skid on ice.
2. Your personality is determined by the position of the Sun, Moon, and Planets when you were born.
3. The universe and its contents evolve.
4. God exists.
5. Intelligent Design is science.
Leading up to the Copernican Revolution - QUICK SUMMARY
References:
http://www-gap.dcs.st-and.ac.uk/~kistory/HistTopics/Greek_astronomy.html#s55
The Great Copernicus Chase - Own Gingerich
Seeds, (see syllabus)
(Note: Western only – Please investigate other cultures)
Greeks (influenced by Babylonian, Mesopotamian, Egyptian, Roman astronomy)
~700 BCE Early astronomy was about time keeping (when to sow and reap crops)*
Greeks ~Fifth Century BCE
What is the sun? How is it related to fire?
What are those tiny lights in the sky?
Why do some lights wander among the others? (5 Planetes*)
Pythagoras of Samos ~500 BCE
Earth is a sphere*
Mathematical perfection* (Note: separation of ideal from reality)
All complex phenomena must result from basic simple ones*
Crystal spheres for Sun, Moon, 5 planets (Egypt, form not substance)
Plato ~360 BCE
Intellectual philosophy to explain universe
From the mathematical perfection, the Heavens are perfect, unchanging*
Therefore, heavenly motion must be in circles and uniform*
Emphasized complex phenomena result from simple ones
Aristotle ~350 BCE
Earth: Corrupt, changeable, imperfect* (Note: Separation of heavens and Earth)
Argued for Geocentric model of universe*
No parallax of stars*
Moon would be left behind*
Side comment: Knew Earth was round (eclipses, ships, southern stars)
Aristarcus ~300 BCE
Heliocentric solar system*
Measured size of Sun and knew that it was substantially larger than Earth
Measured that Sun was much further away than Moon
Hipparchus ~250 BCE
First comprehensive star catalog*
Magnitude scale (1 to 6)*
Ptolemy ~140 AD
Almagest*
Mathematical model of Geocentric universe*
Epicycles (retrograde motion)* (Demos here)
Dark Ages
Roman libraries sacked, plague, rise and fall of Islamic science, etc
Some Observations (Any model of the solar system must explain)
Stars, Sun, Moon rise in east and set in west daily/nightly
Retrograde motion of planets
Venus never seen at midnight (always morning or evening)
Copernican Revolution (~1500 to ~1700)
Copernicus ~1500
Heliocentric model of the solar system returns
Still circles, uniform
Brahe ~1570
Equipment
Predict better
Wanted to prove his geocentric model
Kepler
~1600
Mathematical model of the solar system
Galileo
~1600
Developed and used the telescope.
Observations…..
Newton ~1670
Recognized that gravity was universal
Developed laws of motion that worked on Earth and in the heavens
More next time…
Leading up to the Copernican Revolution - More Detail
~700 BCE
Early astronomy was about time keeping (when to sow and reap crops)*
Needed better observations to keep the various calendars synchronized
Hesiad, Works and Days
…when the Pleiades rise it is time to use the sickle, but the plough when they are setting; 40 days they
stay away from heaven; when Arcturus ascends from the sea and, rising in the evening, remain visible for
the entire night, the grapes must be pruned;…
Greeks ~Fifth Century BCE
Difference between living and nonliving
What is the sun? How is it related to fire?
What are those tiny lights in the sky?
Why do some lights wander among the others? (5 Planetes*)
Pythagoras of Samos ~500 BCE
Earth is a sphere*
Mathematical perfection* (Note: separation of ideal from reality)
All complex phenomena must result from basic simple ones*
Crystal spheres for Sun, Moon, 5 planets (Egypt, form not substance)
Plato ~360 BCE
Intellectual philosophy to explain universe
From the mathematical perfection, the Heavens are perfect, unchanging*
Therefore, heavenly motion must be in circles and uniform*
Emphasized complex phenomena result from simple ones
 About perfection from Plato’s Phaedo : The instance taken there is the mathematical relation of
equality, and the contrast is drawn between the absolute equality we think of in mathematics and
the rough, approximate equality which is what we have to be content with in dealing with objects
with our senses.
 About heavenly motion in circles at uniform speed
Eudoxus – concentric spheres
(first model to explain complex heavenly motion with simple model)
Stars, planets, Sun and Moon move around the Earth in crystalline spheres.
The sphere of the Moon was closest to the Earth, followed in order by the spheres of the Sun, then
Mercury, Venus, Mars, Jupiter, Saturn, and furthest away was the sphere of the stars
 About separating thought from measurement
(Plato from the Encyclopedia Britanica)
... the exact sciences - arithmetic, plane and solid geometry, astronomy, and harmonics - would first be
studied for ten years to familiarize the mind with relations that can only be apprehended by thought. Observing the heavens lowers the spirits…
 About complex from simple: Theon of Smyrna wrote: The changing aspects of the revolution of
the planets is because, being fixed in their own circles or in their own spheres whose movements
they follow, they are carried across the zodiac, just as Pythagoras had first understood it, by a
regulated simple and equal revolution but which results by combination in a movement that
appears variable and unequal
 Which led Theon to conclude: It is natural and necessary that all the heavenly bodies have a
uniform and regular movement.
Aristotle ~350 BCE
Earth: Corrupt, changeable, imperfect* (Note: Separation of heavens and Earth)
Geocentric model of universe*
Arguments for geocentric model*
No parallax of stars*
Moon would be left behind*
Side comment: Knew Earth was round (eclipses, ships, southern stars)
Aristarcus ~300 BCE
Heliocentric solar system*
Measured size of Sun and knew that it was substantially larger than Earth
Measured that Sun was much further away than Moon
Hipparchus ~250 BCE
Discovered precession of Earth
Measured length of year to within 6.5 minutes
May have invented trigonometry
Turned astronomy into a practical, predictable science
First comprehensive star catalog*
Magnitude scale (1 to 6)*
Ptolemy ~140 AD
Almagest*
Geocentric model*
Mathematical model of universe*
Perfect Bodies - circles, spheres*
Uniform motion*
Epicycles (retrograde motion)* (Demos here)
Dark Ages
Roman libraries sacked, plague, rise and fall of Islamic science, etc
Some Observations (Any model of the solar system must explain)
Stars, Sun, Moon rise in east and set in west daily/nightly
Retrograde motion of planets
Venus never seen at midnight (always morning or evening)
Copernican Revolution (~1500 to ~1700)
Copernicus ~1500
Heliocentric model of the solar system returns
Still circles, uniform
Brahe ~1570
Equipment
Predict better
Wanted to prove his geocentric model
Kepler
~1600
Mathematical model of the solar system
Galileo
~1600
Developed and used the telescope.
Observations…
Newton ~1670
Recognized that gravity was universal
Developed laws of motion that worked on Earth and in the heavens
More next time…