Transcript lecture04_2014_geo_heliocentric_theoryx

Lecture 4
• Eclipses
• Geocentric vs Heliocentric Theory
•The Nature of Scientific Theories
The Planets
Prof. Geoff Marcy
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Announcements
• Read Chapter 3 !
•Discussion Sections!
Homework Assignments:
- Assignment Chapter 3: Due Fri at 6pm
Get your ABCD cards ready.
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Full Moon today!
Rises at 9:30pm above the Berkeley hills (East)..
Observing Project #1:
Monitoring the Motion of Mars
Chart the position of Mars in the night sky relative to Saturn and the star, Antares.
Observe Mars, Saturn, and Antares in the evening sky three times (at least once per week),
between now (Sept 9) and Sept 30.
Draw a sketch each evening (or take a photo), showing the positions of
Antares, Mars, and Saturn as labeled dots. Record the time and date on the sketch.
After you have made your three (or more) sketches, write one to two paragraphs
explaining your observations of the position of Mars. Did it move?
If so, why did it move the way it did?
Due Thursday, October 2, in lecture.
Location of Antares, Mars, and Saturn
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Location of Antares, Mars, and Saturn
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Location of Antares, Mars, and Saturn
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Location of Antares, Mars, and Saturn
Alpha Libra
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Observing Project #1:
Monitoring the Motion of Mars
Chart the position of Mars in the night sky relative to Saturn and the star, Antares.
Observe Mars, Saturn, and Antares in the evening sky three times (at least once per week),
between now (Sept 9) and Sept 30.
Draw a sketch each evening (or take a photo), showing the positions of
Antares, Mars, and Saturn as labeled dots. Record the time and date on the sketch.
After you have made your three (or more) sketches, write one to two paragraphs
explaining your observations of the position of Mars. Did it move?
If so, why did it move the way it did?
Due Thursday, October 2.
Review of Last Lecture
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Motion of the Night Sky
as hours pass
1. From Berkeley
2. From the Equator
3. From the North Pole
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Berkeley Hills
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Moon: Going through phases
each 29.5 Days (one orbital period)
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If you stand on the Moon, does the Earth
go through “phases” ? Yes !
When Earthlings see a crescent moon, what is the
phase of the Earth, as seen from the Moon?
a. New
b. Crescent
c. Quarter
d. Gibbous
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Eclipses: Solar and Lunar
• What do they look like?
• Why do they happen?
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Solar Eclipse: Moon blocks the Sun
• Moon is in front of Sun.
(Only occurs at new moon.)
• You are in the Moon’s shadow.
within umbra: total solar eclipse
within penumbra: partial solar eclipse
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Solar Eclipse
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2002 total Solar Eclipse
Ceduna, Australia Dec 4, 2002
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Solar Eclipse
1999 Aug 11 from the Russian Mir Space Station
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Solar Eclipses
• Why don’t we have a solar eclipse every new Moon?
Sun
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Total Solar Eclipse
Lusaka, Zambia 2001
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Solar Eclipse in India
24 October 1995
By: Solar Physicsts Wendy Carlos and Fred Espenak
India
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Solar Eclipse
May 20 2012
Two years ago
Sproul Plaza
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Total Solar Eclipse Predictions
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Partial Solar Eclipse
Thursday, October 23
1:53 – 4:30pm
Lunar Eclipses
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A Model of the Solar System:
Earth-Centered
Or
Sun-Centered
?
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We see only
one hemisphere of the Moon
We never see the back side !
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Why?
We always see
the same hemisphere of the Moon
Not Correct Model
Correct Model
Moon
Earth
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Moon
Earth
Why we always see
the same face of the Moon
Rotation period = Orbital period
Not Correct Model
Correct Model
Moon
Earth
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Moon
Earth
model,
i.e. a concept or a theory,
of the Solar System
Build a
Conceptual models must explain all
the motions of the planets,
i.e., a model must explain the “data”. . .
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Planets: Moving relative to the Stars
Obvious to the eye
• Mercury
– Always close to Sun in angular distance
• Venus
– Always bright. Always near Sun— morning or evening “star”
• Mars
– Noticeably orange. Usually moves west-to-east
– But Mars sometimes moves backwards in the sky !
• Jupiter
– Bright. Moves west-to-east against stars.
• Saturn
– Moderately bright. Moves more slowly west-to-east.
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Motion of the Planets Relative to the Earth
during several years
The Sun and planets
seem to orbit the earth
during months and
years .
Earth
See motion of:
Sun
Mercury
Venus
Mars
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The Motion of Planets
• The Planets normally move West to East
against the background stars.
• Why do planets sometimes seem to move
backwards relative to the stars?
• Greeks concluded that the planets orbit the Earth.
Why did smart people conclude this?
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Observed Motion of Mars:
Normal & “Retrograde””
E
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W
To Explain Retrograde Motion
Two Models:
Geocentric
Heliocentric
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Ptolemy’s
Geocentric Model
• Earth is at center
• Sun orbits Earth
• Planets orbit on small
circles whose centers orbit
the Earth on larger circles
(The small circles are
called epicycles)
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In Heliocentric “model”
Retrograde Motion is a Natural Consequence
• Planets usually appear to move
eastward relative to the stars.
• But as we pass by them,
planets seem to move west
relative to the stars.
• Only noticeable over many
nights; on a single night, a
planet rises in east and sets in
west…
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Two Theories::
Earth-Centered Theory
Sun-Centered Theory
Which theory
Seems
“Best” ?
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Choosing the Best Model:
Explaining Retrograde Motion
• Natural result of Heliocentric Model
• Difficult to explain if Earth is at center
The Best “Model” or “Theory” explains
various data and phenomena with the fewest
assumptions.
“Occam’s Razor “: Choose the simplest model that
explains all the data.
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3D “model” of the Solar System
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Why did the Greeks reject the theory
that the Earth orbits the Sun?
• It ran contrary to their common sense:
Every day, the sun, moon, and stars seem to “rotate”
around us. So, we “must be” at the center . . .
• If the Earth rotated, then there should be a
“great wind” as we moved through the air.
• Greeks knew that we should see stellar
“parallax” if Earth orbited the Sun.
• But they could not detect parallax of stars!
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Test the Theory that
Earth orbits the Sun:
Parallax:
Apparent shift of a star’s position due to
the Earth’s orbiting of the Sun.
Greeks didn’t
detect parallax
!
The nearest stars are
much farther away than
the Greeks thought.
The parallax angles of
the stars are so small,
that you need a telescope
to observe them.
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Two Possible reasons why
stellar parallax was not detected:
1. Stars are so far away that stellar parallax
is too small for naked eye to notice.
2. Earth does not orbit Sun; it is the center
of the universe.
Debate about theory:
Earth-centered vs. Sun-centered Planetary System.
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Section 3
Scientific Theory:
What is a good “Theory” ?
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Scientific Thinking
• It is a natural part of human curiosity:
Search for understanding and truths
that explain many facts.
• We draw conclusions based on our experiences.
• Progress is made through “trial and error.”
Hypothesize. Then test your hypothesis.
Eating pasta makes me get fat . . .
Test this hypothesis, by eating lots of pasta.
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Nicolaus Copernicus (1473-1543)
He thought Ptolemy’s
model was contrived.
Artificial construction;
Too complicated.
De Revolutionibus
Orbium Coelestium
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Copernicus’ Heliocentric Model
•Sun
is at center
•Earth orbits like any other planet
•Inferior planet orbits are smaller
•Retrograde motion occurs when we “lap”
Mars and the other superior planets
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Johannes Kepler (1571-1630)
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Kepler’s Laws
1. Each planet’s orbit around the Sun is an
ellipse, with the Sun at one focus.
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Eccentricity of an Ellipse
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Kepler’s 2nd Law
A planet moves along its orbit with a speed that
changes in such a way that a line from the
planet to the Sun sweeps out equal areas in
equal intervals of time.
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Kepler’s 3rd Law
The cube of a planet’s average distance from the
Sun is equal to the square of its orbital period.
(Use units of years and AUs.)
3
a =P
2
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Curiosity Landing on Mars
5 August 2012
Total Solar Eclipse: Aug 21, 2017
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Solar Eclipse:
Aug 21, 2017
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