2. 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.
3. The Scientific Attitude
The scientific attitude is one of
• inquiry.
• experimentation.
• willingness to admit error.
4. 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.
5. Which of these is a scientific hypothesis?
A. The Moon is made of green cheese.
B. Atomic nuclei are the smallest particles in nature.
C. A magnet will pick up a copper penny.
D. Cosmic rays cannot penetrate the thickness of your
textbook.
The Scientific Attitude
CHECK YOUR NEIGHBOR
6. Which of these is a scientific hypothesis?
A. The Moon is made of green cheese.
B. Atomic nuclei are the smallest particles in nature.
C. A magnet will pick up a copper penny.
D. Cosmic rays cannot penetrate the thickness of your
textbook.
The Scientific Attitude
CHECK YOUR NEIGHBOR
Explanation:
All are scientific hypotheses!
All have tests for proving wrongness, so they pass the test of
being a scientific hypothesis.
23. The Motion of the Earth
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.
The Greeks chose not moving.
Correct Method - Wrong Conclusion
24. Aristarchus
310 - 230 BC
Heliocentric model
Determined relative distances between
Sun and Moon
25. The Distance to the Sun
Aristarchus measured to be 87 degrees
Sun Distance = 19 Moon Distance
(today: Sun is about 400 times further away than moon)
Aristarchus of Samos ~ 310 - 230 BCE
First Quarter Moon
Third Quarter Moon
α
26. Ptolemy
(85 – 165 A.D)
Lived in Egypt,
probably Alexandria
Summarized Greek
astronomy in the
Almagest
Geocentric model of
solar system
29. Very complicated – but it worked! (sort of)
http://astro.unl.edu/naap/ssm/animations/ptolemaic.swf
http://astro.unl.edu/animationsLinks.html#ca_renaissance
30. 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.
31. 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
33. 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
35. 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!!!
