Transcript Geocentric vs. Heliocentric - Answering the Debate 2014

The Answer to the Debate
Learning Goals
 Students will:
1) Develop scientific argumentation skills (students will
use Earth-based observations to prove the commonly
understood notion that the sun is in the center of our
universe).
2) Understand that ancient humans could only use
Earth-based observations to understand that our
solar system is heliocentric.
Success Criteria
 Students will display learning goals by:
1) Using research skills to obtain information.
2) Collecting data to disprove the points suggested by
geocentric theory.
I don’t care what your grade 6
teacher told you – but the Earth is
in the center of the Universe and
all other celestial bodies
(including the sun, the planets and
the stars) revolve around the
Earth!
If you don’t believe me, I’ve got proof!
It’s all just common sense – all you have
to do is watch the sky during the day
and night and even collect data for
several weeks.
Let me list the observations you will
make:
1) Over the course of the day we watch
the sun rise in the east, move across
the sky and set in the west – the sun
is obviously revolving around the
Earth!
2) Similarly – during the day and night
we can watch the moon revolve
around the Earth.
3) If we watch the stars
carefully at night, we notice
that they circle around us.
A camera taking a long
exposure photograph of the
sky will produce a picture
with star trails. This
proves that the positions of
the stars are moving around
us from East to West.
Star trails photographed in a
long term exposure near an
astronomical observatory
4) The Parallax Effect
Depending upon
the position of the
Earth in its orbit,
nearer stars should
be in different
positions relative to
more distant stars.
Have you ever
observed this? I
haven’t!
A simple test of the parallax effect is to place your thumb in front of
your face and observe an object with your left eye only. Now switch
to using your right eye only. The object will be in a different position
relative to your thumb. We can see that the building appears to be
in a different place relative to the thumb in the two pictures. The
same thing should happen as the Earth travels in orbit. More
distant stars should appear to be in different positions relative to
closer stars or planets.
5) If we plot the position of planets carefully at night,
we notice that they also move but at a different
(slower) speed than the stars.
6) If the Earth were orbiting the Sun and rotating on
its axis, wouldn’t we be swept away by the wind
and then fly off into space?
7) God created the Earth on the first day but didn’t
create the Sun and Stars until the fourth day. God
created man in his own image and put humans as
the masters of the universe and therefore must
have placed humans in the central location in the
universe
Prove or Disprove my Statement!
1.
2.
Using evidence that can be obtained by looking at the sky,
argue against my claim that the Earth is in the Center of the
Universe (Geocentric Theory).
OR IF YOU REALLY WANT TO - AGREE WITH MY
STATEMENT – but you must add to my argument! (Aristotle
is on my side as well.) I would suggest that you disprove that
the Heliocentric Theory.
We will now head to the library for a research session
Collect evidence from the library and record your facts on
paper. NO plagiarizing! You must put the evidence into your
own words and be prepared to discuss the data in front of the
class.
YOU MUST UNDERSTAND THE DATA IN ORDER TO BE
ABLE TO ARGUE YOUR POINT!!
1)
2)
3)
4)
5)
6)
Sun and Moon revolve around Earth
Stars revolve around Earth
The Parallax Effect is not observed.
Planets move across sky – only slower
We’d fall off the Earth if it was moving in orbit
God created us and put us in the center of the
Universe
This data is included on the Argument Summary
What I need to get from you:
1)
A completed argument summary – a page of written evidence is
sufficient
2)
HOWEVER MUCH GREATER VALUE WILL BE GIVEN TO THOSE
WHO:
provide diagrams or astronomical charts to help prove your point
(make them big enough to show the class)
add clear written support of the arguments you find – you can add
extra pages if you wish!
a)
b)
3)
I will not make life easy for you! Photographs taken from
spacecraft (a picture of the planets revolving around the Sun,
photos from Satellites, pictures from the Mars Rover etc.) make too
simple an argument. Remember – 100 years ago scientists such as
Claudius Ptolemy, Galileo and Copernicus did not have the luxury
of spacecraft and were able to make good arguments on both
sides of this debate. What evidence could an Earth-bound
observer use to convince me that I am wrong!
4)
5)
6)
7)
Reference your work – write down the names of books or
web sites that you used to gain information
YOU MAY WORK WITH A PARTNER – BUT IF YOU DO I
WILL EXPECT MORE WORK!
Prepare to defend yourself IN A SCIENTIFIC
ARGUMENT!
Remember that simple textbook or internet pages
showing photographs are not sufficient. It is likely that
none of you can produce the background facts that
support the Sun-centered theory shown in these pictures.
I need the written explanations to go with your ideas
Need a few research hints to get you
started?
Here are some keywords:
Heliocentric
Geocentric
Copernicus
Aristotle
Ptolemy
Galileo
Parallax
Retrograde Motion
Please submit your assignment before we continue!
Let’s Follow Up on Our Debate
Aristotle vs. Copernicus
Geocentric vs. Heliocentric Views
Geocentric = Earth Centered
Heliocentric = Sun Centered
The Earth-Centered Universe proposed
by Aristotle and Ptolemy
 The Greek philosopher
Aristotle proposed that the
heavens were literally
composed of 55 concentric,
crystalline spheres to which
the celestial objects were
attached and which rotated
at different velocities (but
the angular velocity was
constant for a given sphere),
with the Earth at the center.
The Earth-Centered Universe proposed
by Aristotle and Ptolemy
 The following figure
illustrates the ordering of
the spheres to which the
Sun, Moon, and visible
planets were attached.
 An outermost sphere was
the domain of the "Prime
Mover". The Prime Mover
caused the outermost sphere
to rotate at constant angular
velocity, and this motion was
imparted from sphere to
sphere, thus causing the
whole thing to rotate.
Aristotle, we have a problem!
 Watch the video showing the
 Ancient Astronomers
noticed that while stars
had fixed positions in the
sky, this is not true of the
planets.
 The planets not only
wandered on the celestial
sphere, but occasionally
appeared to stop and
retrace their steps for a
while, sometimes moving
in a great loop, before
advancing once again. This
motion is called
retrograde motion.
motion of Mars in the sky over
several weeks. The position of Mars
is plotted at the same time each
night.
 Note that the position of the stars is
static but that Mars wanders across
the sky in a retrograde path.
The Retrograde Motion of Mars
This pictures shows the location of
Mars over a 14-week period at the
same time of night against an
identical backdrop of stars.
This type of motion can be seen
with the other planets. Such as
this picture of Jupiter.
Note that astronomical data would had to have been collected (at the
same time of night) for years to prove that retrograde motion exists
Aristotle, we have a problem!
Watch the video showing the retrograde motion of Venus in the
sky over several weeks. The second diagram shows that
retrograde motion is due to the fact that each planet is travelling
in its own orbit AND at different velocities (planets closer to the
sun travel faster due to Gravitational effects. Note (in the left
frame) that the apparent size of Venus also changes.
Ptolemy's Model
 The planetary phenomena of retrograde
motion fascinated and frustrated the
ancient astronomers.
 A second century mathematician astronomer-geographer Ptolemy (Claudius
Ptolemy) improved on the theory proposed
by Aristotle by adding the idea of
epicycles and off-center orbits.
 Ptolemy wrote the Almagest. This great
work dominated astronomical thought right
up to the early years of the seventeenth
century.
 Understand that the Ptolemaic model of the
Universe is still Earth-centred, or Geocentric
Ptolemy (c. 87 – 170 A.D.)
This image shows the complex but ingenious system of off-center
orbits and epicycles (smaller circular orbits in which planets
moved as they orbited the Earth). The is the model developed by
astronomer Claudius Ptolemy of Alexandria
The "solution" to the problems with
Aristotle’s model were in the form of
a clever proposal:
1) planets do not travel along the
concentric spheres themselves,
but to circles attached to the
concentric spheres, as illustrated
in the previous diagram.
2) These circles were called
"Epicycles", and the concentric
spheres to which they were
attached were termed the
"Deferents".
Epicycles and Planetary Motion
 The Ptolemaic model was remarkably successful in
predicting where the planets, moon, and sun would
appear in the sky at future dates.
 It was only in the Middle Ages, when Arabian
astronomers had accumulated more accurate
observations of the planets, that the validity of the
Ptolemaic model began to be questioned.
 Only by further complicating the model by adding
epicycles to epicycles and by tilting the orbits was it
possible to explain the latest data. Ptolemy's model was
accepted throughout much of the world for nearly
1,500 years.
The Epicycle Model
 The net effect of the Ptolemaic Epicycle Model is
illustrated in the animation on the next slide.
 As the center of the epicycle (white dot) moves around
the deferent at constant angular velocity, the red
planet moves around the epicycle, also at constant
angular velocity.
 The apparent position of the planet on the celestial
sphere at each time is indicated by the line drawn from
the earth through the planet and projected onto the
celestial sphere.
 The resulting apparent path against the background
stars is indicated by the blue line.
The Epicycle Model
http://csep10.phys.utk.edu/astr161/lect/retrograde/aristotle.html
Aristotle, Aquinas and the Church
 By the Middle Ages, the ideas of Ptolemy
St. Thomas Aquinas (12251274) – Italian born
Dominican Friar and one of
the greatest Theologians of
the Catholic Church. His
word carried a lot of weight
in the Church.
took on a new power as the philosophy of
Aristotle (newly rediscovered in Europe)
was added to Christian Medieval theology
 This great synthesis of Christianity and
(Aristotle’s) Reason undertaken by
philosopher-theologians such as Thomas
Aquinas.
 The Prime Mover of Aristotle's universe
became the God of Christian theology,
the outermost sphere of the Prime Mover
became identified with the Christian
Heaven
 The position of the Earth at the center of
it all was understood in terms of the
concern that the Christian God had for
the affairs of mankind.
Aristotle, Aquinas and the Church
 Thus, the ideas largely originating with
pagan Greek philosophers were
baptized into the Catholic church and
eventually assumed the power of
religious dogma
 To challenge this view of the Universe
was not merely a scientific issue; it
became a theological one as well
 In the age of the Renaissance,
challenging the views of the church
was considered blasphemy and
subject to great punishment.
 The church was not a benevolent force.
Questioning Aristotle’s model was the
equivalent of questioning Aquinas,
which was the equivalent of
questioning the church (= blasphemy)
The Copernican Model:
A Sun-Centered Solar System
 The Earth-centered Universe of Aristotle and
Ptolemy held sway on Western thinking for
almost 2000 years. Then, in the 16th century a
new idea was proposed by the Polish
astronomer Nicolai Copernicus (1473-1543).
 In a book called On the Revolutions of the
Heavenly Bodies (that was published as
Copernicus lay on his deathbed), Copernicus
proposed that the Sun, not the Earth, was the
center of the Solar System.
 Such a model is called a heliocentric system.
The ordering of the planets known to
Copernicus in this new system is illustrated in
the following figure, which we recognize as
the modern ordering of those planets.
The Copernican Universe
 In this new ordering the
Earth is just another planet
(the third outward from the
Sun), and the Moon is in
orbit around the Earth, not
the Sun.
 The stars are distant objects
that do not revolve around
the Sun.
 Instead, the Earth is assumed
to rotate once in 24 hours,
causing the stars to appear to
revolve around the Earth in
the opposite direction.
Retrograde Motion of Mars
Ptolemy
Copernicus
Retrograde Motion and Varying
Brightness of the Planets
By banishing the idea that the Earth
was the center of the Solar System,
Copernicus’ idea immediately led to
a simple explanation of both the
varying brightness of the planets
and retrograde motion:
Another problem was also answered
– that of the varying brightness of
the planets!
The planets in such a system
naturally vary in brightness because
they are not always the same
distance from the Earth.
The Copernican Revolution
 Copernicus was able to refute the
long-held notion that the Earth
was the center of the Solar system,
but he did not question the
assumption of uniform circular
motion. Thus, in the Copernican
model the Sun was at the center,
but the planets still executed
uniform circular motion about it.
 As we shall see later, the orbits of
the planets are not circles, they are
actually ellipses. The work of
Johannes Kepler (based on the data
of Tycho Brahe) proved the
elliptical orbits of planets
The Copernican Revolution
 As a consequence, the Copernican
model (and its assumption of uniform
circular motion) still could not
explain all the details of planetary
motion.
 Astronomers following Ptolemy tried
to solve the elliptical motion problem
by using epicycles with epicycles.
 In Science we call models that are
simpler, a more ELEGANT MODEL.
Usually simpler models that explain
all of the facts tend to be more
accepted than very complex models
such as the Ptolemy’s multi-epicycle
model.
The Copernican Revolution
 Copernicus was an unlikely revolutionary. It is believed by many
that his book was only published at the end of his life because he
feared ridicule and disfavor by his peers and by the Church, which
had elevated the ideas of Aristotle to the level of religious dogma.
 However, this reluctant revolutionary set in motion a chain of events
that would eventually (long after his lifetime) produce the greatest
revolution in thinking that Western civilization has seen.
 His ideas remained rather obscure for about 100 years after his death.
Much of Copernicus’ theory was based on data from earlier Islamic
astronomers.
 But, in the 17th century the work of Kepler, Galileo, and Newton
would build on the Heliocentric Universe of Copernicus and produce
the revolution that would sweep away completely the
astronomical ideas of Aristotle and replace them with the modern
view of astronomy and natural science. This sequence is commonly
called the Copernican Revolution.
Been There, Done That
Aristarchus of Samos
The idea of Copernicus was not really new! A sun-centered
Solar System had been proposed as early as about 200 B.C.
by Aristarchus of Samos (an island off the coast of Turkey).
However, it did not survive long under the weight of
Aristotle's influence and "common sense":
Aristotle’s Common Sense:
1) If the Earth actually spun on an axis (as required in a
heliocentric system to explain the diurnal motion of the
sky), why didn't objects fly off the spinning Earth?
2) If the Earth was in motion around the sun, why didn't it
leave behind the birds flying in the air?
How can the Geocentric view of
the universe be disproved?
1.
2.
Sun and Moon revolve around Earth
Stars revolve around Earth
1. Earth (and other planets)
rotate on their own axes – this
refutes for the first two
arguments very easily. The sun
rises in the east and sets in the
west since the planet rotates
counterclockwise.
2. The stars rotate around the
north pole slowly during the
night as the earth spins. Since
the north pole points directly
at Polaris (The North Star), it
does not move.
3. The Parallax Effect is not observed
o
3)
o
Parallax is larger for
closer objects
Review - stars should appear
to change their position with
the respect to the other
background stars as the Earth
moved about its orbit, because
of viewing them from a
different perspective –
Astronomers said that parallax
could not be seen!
NOT TRUE! Since planets and
stars are so distant, the
parallax is very small – BUT IT
IS THERE! It can be
measured with more sensitive
equipment.
The parallax method allowed
Astronomers to measure the
distance to close stars for the
first time.
4)
5)
Planets move across sky, but only slower!
Planets travel in retrograde motions
because of epicycles
4) Planets follow orbits around the
Geocentric
Heliocentric
sun that do not match the speed
of the Earth’s rotation – as a
result planets appear to travel
across the sky more slowly than
the stars.
5) The heliocentric vs. Geocentric
View of the Solar System is a far
more elegant solution to explain
retrograde motion!
5)
We’d fall off the Earth if it was moving
in orbit
 This a response to
“Aristotle’s Common
Sense Argument”
 This objection is not
valid because it
represents an inadequate
understanding of the
physics of gravity that
would only be corrected
in the 17th century.
6) God created us and put us in
the center of the Universe
 This is a classic example of trying to use religion to solve a scientific
argument. Obviously, the Catholic Church of the Renaissance Era
would have been seriously humbled by this mistake and it would have
exposed great weakness in their “heavy handed” approach.
 A much more benevolent Catholic Church today would be far less likely
to make a similar mistake
 HOWEVER, many religious groups continue to put “faith” or a literal
interpretation of the Bible in front of scientific knowledge – for example
the debate over Evolution (by the way the Catholic Church agrees with
this theory and we teach it in Grade 12 Univ. Biology.
 There ARE still supporters of the FLAT EARTH theory still living today.
Modern Astronomy vs. The Church
Galileo recants and his life is spared but he
is placed under house arrest for the rest of
his life.
More Evidence to refute the Geocentric
Theory not included in this presentation
1) Phases of Venus (and other
planets)
o Like the moon, planets
display different phases as
they travel in their orbits
around the sun. Without the
invention of the telescope by
Galileo, the phases of planets
could not be determined.
o Seeing phases of planets
would have helped
astronomers refute the
Geocentric Theory more
quickly.
Phases of
the Moon
 We are very familiar
with the concept of
the phases of the
moon. This diagram
shows why we see
phases of the moon
as it rotates around
us.
 The phases of planets
occur for exactly the
same reason
2. The Ancients knew that
Jupiter was a planet. Planets
with their own moons
suggest that the Earth might
be like Jupiter – just another
planet with moons.
 Galileo first saw the 4 largest
moons of Jupiter in 1610. He
plotted their positions as they
rotated around Jupiter. He
determined that Jupiter had its
own “system”.
 By the way you can see the 4
“Galilean” moons of Jupiter with
just a pair of binoculars.
More Evidence to refute the Geocentric
Theory not included in this presentation
3) In the early 17th century,
Isaac Newton stated the
Laws of Gravity
 These laws were used to
dictate the Laws of
Motion which in turn
helped to explain how
objects in space could
travel in orbital paths.
 Kepler refined the orbital
motion of planets from
perfect circles to ellipses.
Activities
1)
2)
Retrograde Motion Activity
Kepler’s Laws activity (tomorrow)