Transcript Celestial Motions - University of California, Berkeley

Astronomy and Earth & Planetary Science C12
Letters & Science C70
The Planets
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Prof. Michael Manga
Prof. Geoff Marcy
Dione
Against
Saturn
& Ring
Taken:
October 11 2005
Tu, Th 11-12:30 am
VLSB 2050
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Announcements
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• Waitlist: Everyone will get in !
•Read Chapters 1 & 2 .
• Discussion Sections meet this week.
• Homework Assignment: Posted on Web.
• 7 Problems / Questions
• Due: Friday, Tomorrow, Feb 1
• Turn in: Basement of Campbell Hall.
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Telescope Observations Project
Two Parts
1. Make Telescope Observations of two objects
Suggestions: Saturn, Mars, Orion Nebula
Telescope Hours: Tue & Thu 7-8 pm, 7th floor of Campbell Hall
Sketch both objects on 1/2 sheet of paper. Note Date and Time.
2. Mark the position of Mars with a dot,
at three times during the Semester,
early, middle, late. (Use either map.)
Note date of each observation.
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Last Time:
Useful Spherical Coordinate System
The Celestial Sphere
North Celestial Pole
Near the ”North Star”
• Stars “glued” to sphere
• Constellations: Apparent groupings
• North & South “Celestial poles”
• Celestial equator
• Ecliptic:
Sun’s path against the stars
= Orbital plane of Earth
• Celestial Sphere Rotates around us
every 24 hours: As Earth spins
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Motion of the Night Sky
1. From Berkeley
2. From the Equator
3. From the North Pole
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Phases of the Moon
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If the moon were farther away
than the Sun, would it ever be
a crescent?
Today’s Moon:
http://www.calculatorcat.com/moon_phases/phasenow.php?tcv=49
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Moon
Going through phases
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If you stand on the Moon,
Does the Earth go through “phases” ?
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Eclipses:
Solar
Lunar
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Solar Eclipse
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Solar Eclipse at Earth
As seen from the Moon
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Solar Eclipse
1999 Aug 11 from the Russian Mir Space Station
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Total Solar Eclipse
Lusaka, Zambia 2001
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Solar Eclipse
24 October 1995
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By:
Solar Physicsts Wendy Carlos and Fred Espenak
India
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2002 total Solar Eclipse
Ceduna, Australia Dec 4, 2002
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Last Time:
Lunar Eclipse
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Total Lunar Eclipse
September 2002
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We see only
one side of the Moon
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Why we always see
the same face of the Moon
Rotation period = orbital period
Earth
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How to build a
“model” (sketch)
or a “theory”
of the Solar System
It must explain all
the motions of the planets:
the “data”. . .
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Planets: Moving relative to the Stars
Obvious to the eye
• Mercury
– Difficult to see; Always angularly close to Sun
• Venus
– Very bright. Always near Sun— morning or evening “star”
• Mars
– Noticeably orange. Usually moves west-to-east
– Sometimes backwards “retrograde” !
• Jupiter
– Very 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
where we make observations
Sun and planets
seem to orbit the
orbit the earth .
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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””
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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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Earth-Centered Theory
Sun-Centered Theory
Which
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 rotates
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 we orbited the Sun – but they
could not detect it.
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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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Chapter 3:
The Science of Astronomy
We especially need imagination in science.
It is not all mathematics, nor all logic, but
is somewhat beauty and poetry.
Maria Mitchell (1818 – 1889)
Astronomer and first woman
elected to American Academy of
Arts & Sciences
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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 Carbohydrates make me get fat . . .
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Ancient Greek Science
• How did the Greeks lay the foundations for
modern science?
• The Ptolemaic model (theory)
of the Solar System.
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Plato (428 - 348 BC)
• All natural
motion is circular
• Reason is more
important than
observation
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Aristotle (384 -322 BC)
• Physics
• elements
– earth
– water
– air
– fire
– quintessence
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Democritus:
Pre-Socratic Greek philosopher
(460 - 370 BC).
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``There are innumerable worlds of
different sizes. These worlds are
at irregular distances, more in one
direction and less in another, and
some are flourishing, others
declining. Some of the worlds
have no animal or vegetable life
nor any water.”
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Epicurus (341-270 B.C.)
Greek philosopher in Athens where he opened a school of philosophy
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“There are infinite worlds both
like and unlike this world of
ours ... we must believe that in
all worlds there are living
creatures and plants and other
things we see in this world…”
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Eratosthenes (276 - 195 BC)
• He measured the circumference of the Earth.
• The Sun is at the zenith in the city of Syene at noon on the
summer solstice.
•But at the same time in Alexandria, it is 7 from the zenith.
• Eratosthenes inferred that
Alexandria was 7 of latitude
north of Syene.
• The distance between the two
cities is 800 km.
• Dist = 7/360 times the
Earth’s circumference.
• His result of 42,000 km is
very close to the right number:
40,000 km.
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Claudius Ptolemy (AD 100-170)
– Theoretical Model of
planets, Sun, Moon
His model fit the data, made accurate predictions,
but was horribly contrived!
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Nicolaus Copernicus (1473-1543)
He thought Polemy’s
model was contrived
Yet he believed in
circular motion
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 & the other superior planets
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Tycho Brahe (1546-1601)
• Greatest observer
of his day
• Charted accurate
positions of planets
• Observed a nova in
1572
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Johannes Kepler (1571-1630)
• Greatest theorist of
his day
• Imagined planets on
“heavenly spheres”
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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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Galileo Galilei (1564-1642)
• First man to point a
telescope at the sky
• wanted to connect physics
on earth with the heavens
• Dialogue Concerning the
Two Chief World Systems
[written in Italian]
This book got him in trouble with the Church!
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Galileo’s Observations
• Galileo discovered
that Jupiter had four
moons of its own.
• Jupiter was the
center of its own
system.
• Heavenly bodies
existed which did not
orbit the earth.
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Galileo’s observation of the phases of Venus was the
final evidence which buried the geocentric model.
Geocentric
No gibbous or full phases!
Heliocentric
All phases are seen!
Galileo observed all phases!
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The Scientific Method
1 Question
2 Hypothesis
– a tentative explanation
3 Prediction
4 Test
5 Result
– confirm, reject, or modify
should be the same no matter who conducts the test
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Hallmarks of Good Science
• Science seeks explanations for observed phenomena that
rely solely on natural causes.
• Science progresses through the creation and testing of
models of nature that explain the observations as simply
as possible.
! Occam’s Razor
• A scientific model must make testable predictions that
could force us to revise or abandon the model.
Theory -- a model which survives repeated testing
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Bad Scientific Practice
• pseudoscience – masquerades as science,
but does not follow the scientific rules of
evidence
• nonscience – establishes “truths” through
belief
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Astrology
• Claims to study how the positions of the Sun,
Moon, & planets among the stars influence
human behavior
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Astrology
Theory:
The positions of the planets, sun, and moon
at the time of your birth determine your
personality and your future, day to day.
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Signs of the Zodiac
AQUARIUS January 19-February 17
PISCES February 18-March 19
ARIES March 20-April 18
TAURUS April 19-May 19
GEMINI May 20-June 19
CANCER June 20-July 21
LEO July 22-August 21
VIRGO August 22-September 21
LIBRA September 22-October 22
SCORPIO October 23-November 20
SAGITTARIUS November 21-December 20
CAPRICORN December 21-January 18
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Your Horoscope: All 12 Signs
Jan 31, 2008
1
7
2
8
3
9
4
10
5
11
6
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12
Test of Astrology
• Write your “sign” of the zodiac
on one sheet of paper.
• Choose the horoscope that
best describes your day today
• Write the NUMBER of that paragraph:
1 - 12 on that paper.
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Jan 31, 2008
Your Horoscope: All 12 Signs
1
7
2
8
3
9
4
10
5
11
6
12
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Theory: Astrology works
The horoscope for your sign of the zodiac
allows you to predict your future.
Design a Test:
If Theory is True:
Your horoscope matches your situation
today (challenges, opportunities, experiences) .
Most of you will choose the paragraph corresponding to your
actual sign of the zodiac
If theory is not true.
In that case, your chosen horoscope will be random.
For example, only a fraction of the “Leo’s” will choose their
horoscope.
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Your Horoscope: All 12 Signs
1
Today:
Jan 31, 2008
7
2
8
3
9
4
10
5
11
6
12
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1, 9, 6, all
Your Horoscope: All 12 Signs
1
Today:
Jan 31, 2008
7
2
8
3
9
4
10
5
11
6
12
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11,Addison-Wesley
1, 9, all
What have we learned?
• What is a theory in science?
• A model that explains a wide variety of observations
in terms of just a few general principles, which has
survived numerous tests to verify its predictions and
explanations.
• How were astronomy and astrology related in the past,
and are they still related today?
• Astronomy and astrology both grew out of ancient
observations of the sky. Astronomy grew into a
modern science. Astrology has never passed
scientific tests and does not qualify as science.
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What have we learned?
• How can we distinguish science from nonscience?
• It’s not always easy, but science generally exhibits at least three
hallmarks. (1) Modern science seeks explanations for observed
phenomena that rely solely on natural causes. (2) Science
progresses through the creation and testing of models of nature
that explain the observations as simply as possible. (3) A
scientific model must make testable predictions about natural
phenomena that would force us to revise or abandon the model if
the predictions do not agree with observations.
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Astrology:
Asking Critical Questions
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Astrology:
What is the Mechanism
that makes it work?
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