Download Today in class Review: The Sky and Celestial

Review
Science and
History of
Astronomy
Scientific Models
Today in class
Scientific Method
Models/theories/etc.
The story
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Review: The Sky and Celestial Motion
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The Science and History of Planetary Motion
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
Review: Celestial Motion
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Question concepts
Question #1: During a single day or night, the Sun, Moon,
stars and planets all appear to move across the sky together.
Their relative positions change relatively slowly from night to
night.
Question #2: As the Earth orbits the Sun, the night side of
the Earth is oriented in a different direction in space, always
away from the Sun. As a result, at different times of year
different constellations are visible in the night sky.
Question #3: Using a figure like that below, where the earth
may be located in various positions around its orbit,
characterize the location of constellations in the sky at
various times (sunset, midnight, noon). For example, the
constellation directly on the opposite side of the earth from
the sun will be highest in the sky at midnight.
Pisces
Aries
Taurus
Aquarius
Capricornus
Earth
Sun
Gemini
Sagittarius
Cancer
Scorpius
Leo
Virgo
Libra
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Science and History of Astronomy
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
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Science vs. the scientific method
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Intro to scientific models
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The story of the heliocentric model of the solar system
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More about scientific practice
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
The ancient question, resolved in 1600’s
- Apparent Retrograde Planetary Motion
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Planets appear to turn around and back up at certain points
during their movement among the stars.
Due to the motion of the earth and planets around the Sun.
Science vs. the Scientific Method
Review
Science and
History of
Astronomy
Science:
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The body of scientific information (facts and inferences)
and their confidence levels, relationships
The community supporting and refining these ideas
The scientific method:
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hypothesize, test, evaluate, refine, repeat
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The process by which ideas are increased (or decreased)
in confidence level
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Scientific model nomenclature
Review
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Models/hypotheses/theories/laws are largely synonyms
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Distinctions are sometimes made in certain cases, but
these are largely contextual
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in this lecture sun-centered solar system is ”hypothesis”
even though actually proven fact
A model can be both ”right” and ”wrong”
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example: Kepler’s ”laws” of planetary motion are not
physical laws at all, are observed ”empirical” relations
Newton’s theory of gravity is incorrect (Einstein’s is
”better”) but we still call it a theory and call its
constituent principles ”laws.”
Even an incorrect model can continue to have utility
A model can be ”just wrong”
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there are many incorrect models that have no utility
utility = ability to predict outcomes of situations
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
The ancient question, resolved in 1600’s
- Apparent Retrograde Planetary Motion
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Planets appear to turn around and back up at certain points
during their movement among the stars.
Due to the motion of the earth and planets around the Sun.
The Models (at this point ”hypotheses”)
Review
Sun-centered
projection effect
Earth-centered
circles on circles (epicycles)
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Ptolemaic model - c. 100
Based on ideas developed in ancient Greece
Greeks developed both earth and
sun-centered models
Review
Science and
History of
Astronomy
Scientific Models
Earth-centered model favored
because it was thought that the
earth must be static
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Stars don’t shift as Earth moves
- In fact they do, it is just very
small (parallax)
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Movement of Earth is
inconsistent with motion of
objects on Earth
- In fact, Aristotle’s laws of
motion were wrong
Provided reasonably accurate
prediction
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Copernican model - 1500’s
Review
Copernicus formalized existing
proposal in 1500’s to allow better
comparison
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He was convinced sun-centered
provided a simpler explanation
for retrograde motion
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To provide accurate predictions
with circular motions, just as
complicated as Ptolemaic
model (circles on circles were
needed)
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Still concerned about a moving
Earth
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Review
Question concepts
Question #4: A sun-centered solar system had been
considered as a possibility since Greek times, even though it
was disfavored until the 1600s.
Question #5: When Copernicus formalized the sun-centered
solar system, it inferred a different movement in space of the
planets. However, it was not significantly simpler in its initial
form, and also the observations of planet motion at the time
were consistent with either the sun- or earth-centered model.
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Confidence scale
The scale of scientific confidence:
10
measured by multiple
independent parties
conjecture
1
−1
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"reasonable" speculation
tool to help you categorize
scientific ideas
position of idea on scale can
depend on person
Unlikely speculation
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At high levels of confidence,
answer is universal
Disproven
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at lower levels of confidence,
scientists can disagree
Experimental evidence (from multiple
sources) is given the highest conficonfidence at the time because it was
dence
thought self-evident that the earth wasn’t different confidence in trustworthy
moving
and not trustworthy sources of evidence
earth-centered had slightly higher
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Tycho Brahe - late 1500’s
Review
Realized need for more accurate measurements and
performed them
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In the face of competing
theories which are both
unsatisfactory, gather better
data!
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This might point the way to a
theory better than both
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In this case both Ptolemaic and
Copernican models were wrong
in detailed comparisons to data
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Shows importance of technical
capability to advancing
scientific understanding
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Kepler - early 1600’s
By abandoning circles was able to develop a highly accurate
sun-centered model
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Stated in 3 laws (will be discussed more later)
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Orbits are ellipses
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Equal area in equal time (sets orbital speed)
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Quantitative relation between period and orbit size
When Tides Change in Science
Review
The new precision of Tycho’s measurements (facts) made a
earth-centered solar system an unlikely inference.
Kepler’s laws, which were sun-centered, provided a more
compelling inference because they were very consistent with
Tycho’s observations of planet motion in the sky. This drove
a historical shift in opinion toward a sun-centered solar
system.
Elevated the confidence of sun-centered model over
Earth-centered.
But the motion of the Earth had not been detected (actually
it wouldn’t be until the 1800’s).
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences
Facts and Inferences
Facts:
Inference can’t have higher
confidence than facts on
which it is based, and may
have much lower
10
−1
observations
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bare results of experiments
(what happened)
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measured by multiple
independent parties
conjecture
1
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"reasonable" speculation
Unlikely speculation
Disproven
line can get blurry for extremely
well tested ”theories”
Example: the motion of the
planets in the sky
Inferences:
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often first called ”hypotheses”
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may have very high or low
confidence
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Example: (historically) the
motion of the planets/sun in
space
Review
Science and
History of
Astronomy
Scientific Models
Scientific Method
Models/theories/etc.
The story
The planet problem
Ptolemy
Copernicus
Confidence scale
Tycho
Kepler
Facts and inferences