Transcript The Scientific Attitude CHECK YOUR NEIGHBOR

Ancient Astronomy
Astronomy – the most ancient of
the sciences
Astronomical records back to
prehistoric times
Scientific Methods
—Common Steps
1. Recognize a question, a puzzle, or an unexplained
fact.
2. Make a hypothesis (educated guess) to resolve the
puzzle.
3. Predict consequences of the hypothesis.
4. Perform experiments or make calculations to test
the predictions.
5. Formulate the simplest general rule that organizes
the three main steps.
The Scientific Attitude
The scientific attitude is one of
• inquiry.
• experimentation.
• willingness to admit error.
The Scientific Attitude
• Fact is a close agreement by
competent observers who make a
series of observations about the
same phenomenon.
• A scientific hypothesis is an
educated guess that is only
presumed to be factual until
supported by experiment.
The Scientific Attitude
CHECK YOUR NEIGHBOR
Which of these is a scientific hypothesis?
A.
B.
C.
D.
The Moon is made of green cheese.
Atomic nuclei are the smallest particles in nature.
A magnet will pick up a copper penny.
Cosmic rays cannot penetrate the thickness of your
textbook.
The Scientific Attitude
CHECK YOUR NEIGHBOR
Which of these is a scientific hypothesis?
A.
B.
C.
D.
The Moon is made of green cheese.
Atomic nuclei are the smallest particles in nature.
A magnet will pick up a copper penny.
Cosmic rays cannot penetrate the thickness of your
textbook.
Explanation:
All are scientific hypotheses!
All have tests for proving wrongness, so they pass the test of
being a scientific hypothesis.
Oldest star chart- 32,000 years ago
(Orion?)
Stonehenge – 3100 – 2100 BC
Great Pyramid at Khufu (Cheops) – 2600 B.C.
Aligned within 1/20 degree of true north
Possible correlations with astronomical objects?
Chichen Itza – Mayan observatory
Medicine Wheel – Northern Wyoming
Chaco Canyon – supernova of 1054?
Chaco canyon – Anasazi sun dagger –
A.D. 400-1300, marks summer solstice
Constellations
Apparent groupings of stars – relatively fixed positions
Constellations – the 88 semirectangular regions that make up the sky
Star trails
Star trails around South Celestial Pole (Gemini Observatory, Chile)
Most of modern astronomy and cosmology comes
from the Greeks
Celestial Sphere
The Geocentric View
Aristotle’s View: The
Most Perfect Form is
the Circle
The Crystalline Spheres
The Motion of the Earth
Correct Method - Wrong Conclusion
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Parallax: The apparent motion of an object
due to the motion of the observer.
The Greeks could not detect any parallax for
the stars (or planets).
Conclusion:
– The Earth is not moving.
OR
– The Stars are too far away to measure parallax
with crude instruments / eye.
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The Greeks chose not moving.
Aristarchus
310 - 230 BC
Heliocentric model
Determined relative distances between
Sun and Moon
The Distance to the Sun
Aristarchus of Samos ~ 310 - 230 BCE
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Aristarchus measured  to be 87 degrees
Sun Distance = 19 Moon Distance
(today: Sun is about 400 times further away than moon)
First Quarter Moon
α
Third Quarter Moon
Ptolemy
(85 – 165 A.D)
Lived in Egypt,
probably Alexandria
Summarized Greek
astronomy in the
Almagest
Geocentric model of
solar system
Epicycles and Equants
Everything circles something else…
Very complicated – but it worked! (sort of)
http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf
http://astro.unl.edu/animationsLinks.html#ca_renaissance
Major assumptions of the Ptolemaic
model
– All motion in the heavens is uniform
circular motion.
– The objects in the heavens are made from
perfect material, and cannot change their
intrinsic properties.
– The Earth is at the center of the Universe.
After the Greeks:
• Alexandria burns in 272 A.D., Roman empire
collapses, and Europe enters Dark Ages
• Roman Catholic Church combines Ptolemaic with
Aristotelian thought into official church doctrine –
Earth as immovable center of cosmos
• Much of astronomy is carried forth by Persian and
Islamic astronomers who preserved Greek thought
and refined it – named many stars we know today
Breaking through the old model…
Major problems with the Ptolemaic
System:
It failed to….
Accurately predict eclipses (off by hours, days, etc…)
* Predict position of planets accurate enough
*Couldn’t explain meteors, comets, supernovae
Nicolas Copernicus (1473-1543) – proposed heliocentric
hypothesis, mostly on philosophical grounds
Copernicus’ model:
• Gave similar predictions to Ptolemaic
model, also used epicycles, etc…
• Proposed earth rotates on axis to cause
night and day
• Proposed earth and other planets travel
around sun
• Radical idea for time –this sounded crazy to
most people!!!
De Revolutionibus Orbium Coelestium, 1543
(On the Revolutions of the Heavenly Spheres)
Copernicus’ explanation of
retrograde motion
Galileo
1564 - 1642
• All bodies fall at same rate!! - Tower of Pisa
Galileo’s Telescope
• Galileo’s telescopic observations led
him to firmly reject the geocentric
model.
The Milky Way was composed of millions of stars.
He realized that wherever he looked, he saw more
and more stars……
Saturn
Galileo noticed….“Saturn has ears”
Sunspots
A. The surface of the Sun was imperfect.
B. apparent motion of the spots across the Sun's disk implied
rotation.
• Detailed moon drawings – the moon is
not a smooth sphere!
The Galilean Satellites
• They Orbit Jupiter!
•So Why Cannot the Planets
Orbit The Sun
The Phases of Venus
Galileo noticed that when Venus wanes (becomes crescent), it becomes
larger.
The Phases of Venus