Remember, you have a

1
Remember, you have a Reading Assignment
Read Chapters 2-4. Ensure that you a) know the
items listed in the Summary Of
Key Concepts. b) understand the concepts
described in the Common Misconceptions
boxes. Expect a quiz on Chapter 4 on Monday
(Jan. 21)!!
2
Announcement
Another opportunity for extra-credit.
If you attend a session at the new MacAdam
Student Observatory you will get an additional 5
points added to your final grade. Date Time
Slots 2/06 800, 900, 1000 3/05 800, 900,
1000 4/01 900, 940, 1020 4/21 900, 940,
1020 Send me an email with four choices of
dates/time slots.
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What causes the seasons?
Many of you think that its because the Earths
orbit is elliptical, and therefore the Earths
distance from the sun varies.
Thats NOT the reason!
Some of you think that since the Earths axis of
rotation is tilted relative to the ecliptic, the
distance between each hemisphere and the sun
varies.
Thats NOT the reason!
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What causes the seasons?
The Earths axis of rotation is tilted relative
to the ecliptic. This means that (except for
during the Spring and Fall equinoxes) one
hemisphere gets more direct sunlight than the
other.
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What causes the seasons?
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What causes the seasons?
Our summer (Northern hemisphere)
Our winter (Northern hemisphere)
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What causes the seasons?
Why is the Summer Solstice the start (instead of
the middle) of summer?
Does orbital distance affect the seasons?
If so, wed expect the Northern Hemisphere to
have less intense seasons than the Southern
Hemisphere. But this doesnt happen why?
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Question What would happen if the Earth
wasnt tilted?
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Of course were not the only planet with seasons.
The Seasons of Saturn Credit R. G. French
(Wellesley College) et al., Hubble Heritage Team
(AURA / STScI / NASA)
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Hallmarks of science
Science
seeks explanations for observed phenomena that
rely solely on natural causes.
creates and tests models of nature that explain
observations as simply as possible.
makes testable predictions about natural
phenomena that would force us to revise or
discard the model if the predictions do not agree
with observations.
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The Scientific Method
make observations
ask a question
make a hypothesis
make a prediction
test the prediction
If the test does not support the hypothesis,
revise or make a new hypothesis. If the test does
support the hypothesis, make more predictions,
and perform more tests.
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The Scientific Method
Is Intelligent Design science?
Is String Theory science?
Is Many Worlds Theory science?
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Theory
A theory is a hypothesis that has survived
repeated and varied testing.
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The Scientific Method
Is Evolution a theory?
Is String Theory a theory?
Is Relativity a theory?
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Ancient Astronomy
Astronomy appears to have started as a very
practical science.
Astronomy was used to predict the seasons.
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Phases of the Moon
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Phases of the Moon
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Ancient Astronomy
Astronomy was used to tell the time of day.
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Ancient Astronomy
Astronomy was used for navigation.
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Ancient Astronomy
The Earth is a sphere Pythagoras because
spheres are perfect. Aristotle because the
earth casts a round shadow.
The Earth isnt actually a sphere its an oblate
spheroid.
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Ancient Astronomy
Eratosthenes determined the circumference of the
Earth (probably to an accuracy of 5).
How did he do it?
Following the scientific method, what would be a
good set of subsequent measurements?
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Copernican Revolution
Copernicus (1473 - 1543) proposed a helio-centric
model of the universe. Why did he do such an
outrageous thing?
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Copernican Revolution
Copernicus (1473 - 1543) proposed a helio-centric
model of the universe. Why did he do such an
outrageous thing?
Why does this mark the start of modern science?
The title of his final work was De Revolutionibus
Orbium Caelestium. What are the orbs that he
mentions?
What was the major shortcoming of Copernicus
description of the solar system?
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The Scientific Revolution Continues
Kepler (1571 - 1630) proposes three simple laws
(now known as Keplers laws of planetary motion).

• The orbit of each planet around the Sun is an
  ellipse, with the Sun at one focus.
• As a planet moves around its orbit, it sweeps out
  equal areas in equal times.
• More distant planets orbit the Sun at slower
  average speeds, obeying the precise mathematical
  relationship
• p2 a3
• where p is the orbital period in years and a
  is the average distance from the sun in
  Astronomical Units.

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The Scientific Revolution Continues
Galileo (1564 - 1642) strengthened the claim that
the Earth orbits the Sun.
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The Scientific Revolution Continues
Amicus Plato amicus Aristoteles magis amica
veritas.
Newton (1642 1727) discovered a simple set of
laws that govern all motion sort of.
Newton was also responsible (along with Leibniz)
for the initial development of calculus.
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Rules of Reasoning in Philosophy
Rule 1 We are to admit no more causes of natural
things than such as are both true and sufficient
to explain their appearances.
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Rules of Reasoning in Philosophy
Rule 2 Therefore to the same natural effects we
must, as far as possible, assign the same causes.
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Rules of Reasoning in Philosophy
Rule 3 The qualities of bodies, which admit
neither intensification nor remission of degrees,
and which are found to belong to all bodies
within the reach of our experiments, are to be
esteemed the universal qualities of all bodies
whatsoever
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Rules of Reasoning in Philosophy
Rule 4 In experimental philosophy we are to look
upon propositions inferred by general induction
from phenomena as accurately or very nearly true,
notwithstanding any contrary hypothesis that may
be imagined, till such time as other phenomena
occur, by which they may either be made more
accurate, or liable to exceptions.
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The Scientific Method
make observations
ask a question
make a hypothesis
make a prediction
test the prediction
If the test does not support the hypothesis,
revise or make a new hypothesis. If the test does
support the hypothesis, make more predictions,
and perform more tests.
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The Scientific Method