CASE STUDY
Teaching Nature of Science Through
Scientific Models: The Geocentric vs.
Heliocentric Cosmology
By Matthew Price and Michael Rogers
I
n the nonmajor science classroom,
case studies—when used as learning tools—should help students
build the necessary framework for
us to help them build an understanding of the nature of science. For most
students, the nonmajor science course
(in our case, Astronomy 101) may
well be the last time that they interact with science in a formal learning
setting. In their 1998 study, Abd-ElKhalick, Bell, and Lederman found
that many teachers believe that they
are teaching nature of science through
activities when they are mostly concentrating on the content and little
on the processes that led to our understanding of the content. As Ryder,
Leach, and Driver (1999) noted,
nature of science consists of understanding many different facets of science. For example, the nature of science also includes scientific practices
such as peer review, mutual criticism,
or grant writing and science–society
interactions to including the historical, ethical, and economic dimensions
of science (National Science Teachers
Association, 2000; American Association for the Advancement of
Science, 2009). Knowledge of the
methods and concepts used by scientists are often elements of science
instruction, yet they are rarely treated
as an integrated process by which scientific knowledge is developed, used,
and modified. Therefore students
in the college classroom have epistemic frameworks that do not reflect
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Journal of College Science Teaching
the underlying nature of scientific
knowledge (Abd-El-Khalick, 2004).
The study by Abd-El-Khalick (2004)
indicated that students think that science itself progresses in an enumerated scientific method, with each step
needing to be done before continuing
to the next step. Often in the introductory science courses with laboratory
exercises, this is the way that students
are instructed, so their framework is
supported by the instruction.
At Ithaca College, we’ve been conducting a National Science Foundation–funded project (DUE#0536246)
that examines methods of helping
students understand the nature of
science and build an appropriate
epistemological framework. We have
explicit discussions about the nature of
science with the students and the “values and beliefs inherent to scientific
knowledge” (Lederman, 2004) to include science–society interactions. The
connection between the process and
the products of science are discussed
directly and embedded in examples
and activities. This framework is based
on the work by Lederman (2004), in
which he introduces the seven aspects
of the nature of science: that science (a)
is tentative, (b) is empirically based, (c)
is subjective, (d) involves imagination
and creativity, (e) is socially and culturally embedded, (f) treats observation
and inference differently, and (g) has
theories and laws that are different but
contain similarities. Lederman (2004)
also advocated for using the term
nature of science instead of the nature
of science because no consensus presently exists on a single definition for
the nature of science.
We have found the discussion
of and activities concerning the
construction of scientific models
particularly effective in helping
students understand the nature of
science. We share here the first of
many model building exercises. The
first is a mock debate-style introduction to applying current evidence to
building a scientific model. Most
introductory astronomy textbooks
begin with a review of ancient
Greek astronomy, often starting
with Aristotle and a brief nod to
the Babylonians. Our students have
likely learned about the Sun-centered
(heliocentric) universe in middle or
high school. Engaging students in a
debate between an Earth-centered
(geocentric) universe and a Suncentered (heliocentric) universe can
help them better understand why the
Greek’s geocentric model matched
observations of the time.
The model building
To present a consistent approach to
building scientific models we use the
same algorithm with different topics
such that early on in the semester,
students can begin to think about our
approach. The algorithm is:
Introduce the concept: The students read about the topic prior to
FIGURE 1
When introducing the concepts
of the nature of science and how
one builds a model, we have found
success in discussing directly with
students the frameworks from Ryder
et al. (1999) and Lederman (2004).
The students are given the definitions and some examples of each of
the seven aspects of science given
PHOTO COURTESY OF THE AUTHOR
attending a class period where thinkpair-share (Lyman, 1987; Mazur,
1997) questions about the concept
are punctuated by mini-lectures when
needed. This may be a list of observations needing to be explained, a
set of definitions that will need to be
used, or other important aspects of the
concept such that the students create
an advanced organizer for the rest of
the instruction.
Group discussions of the historical
alternatives: Most successful modern
scientific models have had one or
more competing models that were
shown to be less robust as more evidence was gathered. The Geocentric
and Heliocentric cosmologies are
prime examples of this idea. This
discussion can take from 15 minutes
to an entire class period.
Group discussions of scientific
decision making: Discuss why we
discarded the alternate and kept the
original model, modified the original
model, or discarded the original model in favor of the alternate model. In
the case presented here, the evidence
that the Greeks had at the time was
not compelling enough to abandon
the Earth-centered universe.
Move forward through time: Minilecture on how technology and society
can create new experimental opportunities that can help revisit the
model such that it can become a more
complete explanation of the physical
world, and an explicit discussion of
the nature of science elements.
Students participating in an inquiry lab in the performance-based
physics classroom at Ithaca College. This room has 11 tables that seat
9 students. We use the organization of the tables to create working
groups for the Helio-Geo centric universe discussion.
by Lederman (2004), with some additions from Sagan (1995). That all
ideas obeying our scientific principles
are equally valuable at the beginning of the model-building process
is stressed throughout the course. As
evidence is accumulated, those ideas
with no evidence must be discarded
for now and only those ideas with evidence remain. As students build their
evidence-based models and present
them to the class, the instructor acts
as a facilitator who points out that
the students, and scientists, may have
two strong ideas at some point where
the evidence seems to support both
models. Through the use of Occam’s
razor and student polling, the class
tries to reach consensus in choosing
the explanation that is the simplest.
To set the stage for the rest of
this discussion, we need to describe
the classroom where this instruction
takes place. The classroom that our
introductory astronomy course takes
place in is based on the SCALE-UP
classroom developed by Beichner
(2006). Figure 1 shows the layout of
this room. The room has eleven twometer-diameter tables located about a
media/teaching console. Each table is
equipped with three laptop computers
for students to record data, write reports, or watch media demonstrations.
There are nine chairs at each table,
allowing groups of three to work
together. The tables are set such that
the entire table can also engage in a
conversation while working on large
group assignments.
In this classroom arrangement, the
instructor is able to assign projects or
tasks to the class and progress from
table to table during the work. Demonstrations that are normally done by
the professor at the front of the lecture
hall can be turned into table-top experiments for the students. The intent
for this classroom orientation is to
create a student-centered environment
and actively engage the students in the
class. The structure of our classroom
allows us to have 99 students in an
active learning environment where we
Vol. 46, No. 2, 2016
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CASE STUDY
can move easily from lecture to activity, and from individual student work,
to group work, to entire table work
(Kregenow, Rogers, & Price, 2011).
To prepare for the Geo-Helio activity, students respond to think-pair-share
questions or statements that act as an
advanced organizer. These statements
and questions ask the students to commit to some understanding of the way
that science uses evidence to build its
models and how and what those models might be. Examples follow:
• Scientific models are always true
and accurate representations of
the real physical world.
• Models that are incorrect will be
immediately abandoned.
• The Earth-centered model of the
universe is wrong and cannot be
used to gain any knowledge of
the universe.
• Given the observational evidence
that we have so far in class we
would describe the universe as:
○ Sun-centered
○ Earth-centered
○ Both
○ Neither
The last question is based on an observational description of the night
sky that has taken place for the previous two class meetings.
While the students are working on
the questions, a classroom helper (an
undergraduate teaching assistant in
our classroom) hands out 10 prepared
index cards (one per table) with 5 of
one color for the Geocentric tables and
5 of another color for the Heliocentric
tables. Note that during this particular
activity, we have students arrange
themselves so that an even number
of tables are occupied. A short lecture
sets the stage for the model-building
activity and acts as a transition from
the think-pair-share activity:
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Journal of College Science Teaching
We are in Greece approximately
2,000 years ago. We do not
have any technology or findings
available to us that would not
be available to the Greeks. This
means that all of our evidence
can only be collected with our
eyes. Five of the tables are
believers in the Geocentric
cosmology and five are believers
in the Heliocentric cosmology.
The students are told to read their
card. Each card contains a statement
and the argument that might be made
for that statement. The students are
instructed to think of an experiment or
experiments that might be conducted
to gain evidence in favor of the argument on their index card. While the
students are listing possible experiments, we alert them to the fact that
we have rigged the system a bit. We
tell the students that we’ve picked
certain arguments and evidence, while
ignoring others. This was done to
simplify a rather complex scientific
debate to allow the class to focus more
on model building.
The cards that are handed to the
tables are:
• Describe your model: Talk about
your cosmology and what that
means for the motions that we
see the stars make in the sky.
• The Moon problem: Both groups
agree that the Moon orbits the
Earth or we wouldn’t have Moon
phases. How come the Moon is
not left behind by the Earth if the
Earth is moving?
• The Parallax problem: We don’t
measure stellar parallax with the
naked-eye. We would expect to
see stellar parallax if the Earth
moved.
• Motion problem 1: For the Sun
to rise and set, the Earth should
spin. How come we do not feel
that motion, experience a great
wind opposite the direction of
the motion, or we do not see the
birds left behind when they are
no longer sitting on the ground?
• Motion problem 2: To see
Seasons, the Earth should orbit
the Sun faster than the Stars.
How come we do not feel that
motion, experience a great
wind opposite the direction of
the motion, or see the birds left
behind when they are no longer
sitting on the ground?
The students spend approximately
20 minutes generating experiments to
support their argument. While the students are working, the instructor and
teaching assistant move throughout
the room listening, prompting, and answering questions. It is important that
the instructors don’t fall into giving
mini-lectures at each table, but rather
serve as a guide to the activity. While
the students are developing an argument from their cosmology that could
possibly be tested, it becomes clear to
the Heliocentric tables that their task is
daunting. They begin to realize that the
rules of the activity do not give them
any of the physics or technology available that would make it possible to do
experiments in support of their model.
The Geocentric tables, however, have
an easy time by mostly saying “go
outside and look for yourself.”
After the students at the tables
have identified their experiments, a
representative for each table is elected
and each table reports their findings.
After the representative delivers the
argument (normally no more than
one minute) the instructor asks the
questions, “Does this argument fit
the observations that we can make?”
(The answer is either yes or no.) “Can
we accomplish the proposed experi-
ment?” Through this questioning the
students are reminded that we are in
Greece approximately 2,000 years
ago and the Geocentric cosmology is
the accepted model, and the Heliocentric cosmology is the alternate model.
After all of the tables have presented, we look at a tally for each
argument. We notice that there are
some good arguments for the Heliocentric cosmology, but they are not
strong enough at this time to abandon
our currently working Geocentric
cosmology. We Greeks will accept
the geocentric cosmology. This introduces a good point to discuss with
the students —the tentative nature of
science. Our Geocentric cosmology
is not complete, and the Heliocentric
cosmology has some merit. If the
evidence were more complete, we
Greeks would agree that the Heliocentric cosmology is the better model.
The activity concludes with a
discussion of a model that explains
a phenomenon but may not correctly
explain the underlying nature of the
phenomenon. This discussion uses
the Geocentric model and reviews the
numerous predictions this model correctly makes, but yet the underlying
premise that the Sun revolves around
the Earth is completely wrong. A model of what is truly happening may take
many centuries to develop, and you
might come back to one of the models
that we had earlier put to the side. In
the case of the Geocentric cosmology,
it took the observations of Galileo to
show that each of the Geocentric arguments could be proven false. Yet to
this day when we first teach students
to look at the night sky, we do so from
a Geocentric perspective.
This exercise is indeed a straw
man set up on our part. We believe
that the students are told conflicting
ideas about the early astronomers in
an unconvincing way. When many
texts bring up the discussion about the
dawn of scientific thinking, students
will read that the Greeks gave us our
ideas for thinking scientifically, but
that they got their cosmology wrong.
A question in the texts may by on
the order of, “How could the Greeks
get their cosmology so wrong?” The
purpose in the text is to lead into the
discussion of the lack of technology.
That it was really the dawn of better
observations that led us away from
Aristotle’s and Ptolemy’s cosmologies. However, Aristarchus, Philolaus,
and other contemporaries of Aristotle
offered heliocentric points of view. I
try to show with this straw man approach that it is not out of the realm
of rhetorical argument that Aristotle
could argue the preponderance of
evidence for his cosmology over that
of Aristarchus. Yet later in the semester, as we move into the discoveries
of Brahe and Kepler, the work by
Copernicus, and the work by Galileo,
we note that there is a technological
advance. But we remind the students
that as astronomers we also assume
a geocentric point of view when we
make measurements. This indicates
that even when previous models are
shown to be false, we don’t abandon
them completely, and that now it is
common for the term geocentric or
heliocentric to indicate a coordinate
system for the student.
Data were taken during the Spring
and Fall semesters in 2009. Students
were given the following question
during an exam period:
In no more than two sentences
explain why the Greek scientists
would accept the Earth-centered
universe over the Sun-centered
universe. Do not talk about the
different specific arguments, just
talk about what would make the
scientific Greeks choose a model
that does not explain what is
really happening.
The exam question was graded on
a 20-point scale by one of us teaching
the course. The exam took place two
weeks after instruction. In spring 2009,
the average score for the exam question was 16/20, with 50% of the class
scoring at 18 or better and 20% scoring
below 10/20. In fall 2009, the average
score for the students was 17/20, with
60% of the class scoring 18 or better
and 10% scoring below 10/20.
When we looked at the responses
for those scores of 18 or better we
found common phrases; “they didn’t
have the technology” and “the observation fit Sun-centered better.”
Our common theme of how to pick
between competing models revolves
around which model better explains
the observations and what would a
scientist need to make a measurement
that might refute the current accepted
model. Students that scored lower
than 10/20 did not use these phrases
and commonly said “it looks like the
Sun is moving and we are sitting still,”
without discussing why this observation would be important.
Discussion
The nonmajor science course is an
opportunity for instructors to help
students interact with the process
and products of science for, what is
likely, the last formal time to do so.
Using case studies to show students
how scientific models are built may
help students gain a deeper understanding of how and why we choose
one idea over another. Our project
is conducting pre/posttesting using
the Views on the Nature of Science
instrument (Lederman, Abd-El-Khalick, Bell, & Schwartz, 2002) and selective interviews based on the Student Understanding of Science and
Vol. 46, No. 2, 2016
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CASE STUDY
Scientific Inquiry instrument (Liang
et al., 2006) to better understand how
our efforts are helping students form
a better understanding of the nature
of science (Kregenow, Rogers, &
Constas, 2010). Both of these instruments are showing shifts from novice thinking to more sophisticated
views of the nature of science. However, these shifts in understanding
are not as strong as we expected. We
are currently looking at possible limits to the measurement instruments,
while also examining each of Lederman’s seven aspects of the nature
of science to see if certain items are
more resistant to change. Our measurement instruments have shown
that discussions of the difference and
similarities between theories and
laws to be particularly problematic.
We suspect that these two words
have such a wide variety of colloquial uses that their scientific meaning (even among scientists) may be
lost. We are particularly interested in
the hierarchical perspective to theory and law (e.g., over time theories
eventually become laws) that leads
to statements such as “XYZ is just
a theory and not a fact.” The National Science Teachers Association’s
(2000) position piece on the nature
of science and the Next Generation
Science Standards (NGSS Lead
States, 2013) both put forward clear
definitions of theory and law and dispel the hierarchical nature that theories are eventually promoted to laws.
Seeing as how some of the students
in our Astronomy 101 course will go
on to be childhood and adolescence
educators, we think it important to
keep working on this issue. In contrast, our students generally leave
our course having a more sophisticated understanding that culture and
society have an impact on the nature
of science. ■
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Journal of College Science Teaching
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Matthew Price ([email protected]) is an
assistant professor and Michael Rogers
([email protected]) is a professor, both
in the Department of Physics and Astronomy at Ithaca College, Ithaca, New York.
Reproduced with permission of the copyright owner. Further reproduction prohibited without
permission.