On August
16th, a panel convened by the International Astronomical Union in an attempt to vote
on the definition of what a planet is. In doing so, they raised the possibility of increasing the number of planets from nine
to twelve. Imagine--adding three planets to the solar system with the stroke
of a pen. What a thrilling opportunity for science teachers, and for so many
reasons. The vote raised a lot of questions and has been followed by a week of controversy. Today, the definition of "planet" may finally be decided.
When you
think about it, science teachers probably spend too much time filling
children's heads with science facts. Our textbooks are overstuffed, our
assessment systems emphasize memorization over critical thinking, and we
struggle to find time for inquiry. For decades, we've been telling our students
"there are nine planets in our solar system" rather than "nine objects in our
solar system meet our current definition of a planet." We shouldn't be
surprised that students struggle to understand scientific knowledge as a
social, human construct. But the IAU panel's recommendation gives us an
opportunity to engage our students in conversations about what science is and
how it works.
As
teachers, do we want our students to walk away from our classrooms thinking
that scientists know all there is to know about a field of study? Or do we want
them to view science as an organic, evolving pursuit of understanding? In order
for students to understand science, they need opportunities to examine why
scientific knowledge is subject to revision, and more importantly, the process
through which scientists achieve consensus. The debate about our solar system
gives teachers a great opportunity to showcase science as a social process and
help students understand that scientific knowledge can be tentative.
And let's
face it--teenagers love to argue. Now we can show them that scientists do this
too--they even argue about how we define objects in our solar system! The debate
about what constitutes a planet has lasted for years! Although the panel's
decision pertains to a major issue that is international in scope, scientists
debate and discuss ideas and results in a search for meaning just about every
day. Is this data point anomalous? Is this a valid measurement? Are these
results reasonable? What constitutes a fair test of our hypothesis? Can we
generalize these results to situations that are in some respects dissimilar to
our experiment?
The IAU's recommendation provides a model of the process of
science. Yes, it's a debate about a definition but the simple fact is that
unless we agree on how we will measure something, or what counts as data or
evidence, we'll continue to have difficulty talking about and agreeing upon
what we observe. To quote one of my favorite films, "what we'll have here is a
failure to communicate."
Some may
argue that the definition of a planet is beyond the reach of K-12 students. I
don't think so. Middle school students are fascinated with the "weird and
mysterious." It doesn't take long in science class for them to see that Pluto
is a bit of an oddball--its very distant, its orbit is very tilted, and
sometimes it isn't even the farthest planet from the Sun. I would bet that 99
out of a 100 of my middle school students would challenge Pluto's status under
our previous vague definition of planet.
I see this
as a great opportunity to take advantage of my students' natural curiosity. I
am still thinking about how I'll do this, but I think I'll begin by doing some
activities that help them to appreciate how gravity works (at a level that is
appropriate for them) and the difference between orbit and rotation. Then, I'll
present them with what we know about the planets and say 10 or 15 other solar
system bodies (density, mass, volume, radius, average distance from the Sun,
what the object orbits (the Sun or one of the nine current planets), and so
on). I'll include moons of several planets and the objects that would be
considered planets under the new definition. I might ask my students to work in
small groups to use the information to categorize all of the objects as either
planets or smaller solar system bodies, and to come up with definitions to
support their decisions. I'm sure that there will be differences between how
each group came up with categories and definitions, and that's the teachable
moment. We could set up a panel from each group to debate the proposed
definitions, and hold a closed ballot vote that calls for a unanimous decision.
If a decision isn't reached, the panel members would have to return to their
groups to discuss the merits of the leading contenders, and return to the panel
with recommendations. I'll conclude the unit by presenting the IAU's proposed
definition and recent discoveries about objects that led scientists to
reconsider this question and convene the panel, and asking students to
re-categorize objects using the scientist's current view.
Our science
textbooks will have to be rewritten. What a thrilling opportunity for
educators. No matter how you pursue this news in your science class, I hope
you'll take advantage of this unique news event. Let's help students experience
science as it really is, and show them how new technologies and discoveries not
only give us new evidence and insights into how the world works, but challenge
us to revisit our earlier definitions and ideas. Do our current ideas still
hold up in light of new evidence? Do we really know everything there is to know?
About
the author:
http://www.udel.edu/msmith/vita.html
More
information:
Read it
yourself: the IAU Resolution: The actual text
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_resolution.html
Questions
and Answers about the IAU resolution:
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_Q_A.html
Media/Images/movie
to accompany IAU resolution: http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601a_video.html
Defining Moments: The Saga's History
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