Rotation and Flattening Lesson
Overview
As we observe the thousands of galaxies in the visible universe, we find
that many of them are flattened disks. Because the process of galaxy formation
is too slow to watch, scientists study it with computational models. This
lesson/activity demonstrates how one might explain the appearance of so
many flat galaxies with a computational model.
Preparation and Materials
The teacher should be familiar with the GalaxSee application
(for those unfamiliar with this software, there is an online tutorial),
have it loaded on a PowerMac, and have some means of displaying the monitor
to the class.
If you have configured Netscape to use GalaxSee as a helper
application, then clicking on the names of the galaxy files below should
start
GalaxSee and open those particular galaxy files. Instructions
for configuring Netscape are included with this distribution.
Objectives
Students will
-
use a computational model to discover possible answers to a question about
a natural phenomenon
-
practice accurately observing and recording data from a scientific experiment
-
communicate and defend a scientific argument while collaborating with other
students.
Standards
This lesson fulfills portions of the following standards and curriculum
guidelines:
Activities
-
If the students have not observed through previous activities
the fact that many galaxies (including our own) are flat disks, show them
images of several galaxies (available at numerous sites on the World Wide
Web) and allow them to discover this fact.
-
Make the following points about galaxy formation:
-
The process is extremely slow--it takes billions of years for a galaxy
to form.
-
Because of this, we cannot watch the formation happen.
-
In order to try to understand galaxy formation, scientists model galaxies
on computers and, by watching the model evolve, they hope to learn why
real galaxies have the features that we observe.
-
If we are to accomplish anything in science, it is extremely important
that we are careful observers.
-
With the monitor displayed so that the students can see it, make sure that
the Galaxy Setup is for a spherical galaxy of 256
stars that are
500 solar masses each, with the rotation factor set
to zero. Generate a new galaxy (or use the pre-generated galaxy
"no_rotation.gxy"
at this web site. Run the simulation, and have the students watch what
happens. Rotate the
galaxy for them so they can see it from different angles. Let the simulation
run until the stars clump together in the center. Stop the simulation,
and have the students write (briefly) what they observed.
Note: As the stars clump to the center, their speeds will increase
rapidly, and error will start to accumulate in the model. If this is allowed
to continue, the model will become unrealistic, and could, for example,
throw all of the stars out beyond the original boundaries. This is an inaccurate
result, and if you allow the simulation to run beyond the initial clumping,
you should be sure to discuss the implications of error in the model.
For more information about detecting and controlling error, see the
section about the info window
in the GalaxSee tutorial.
-
Now change the setup described in #3 so that the rotation factor is
1.
Generate a new galaxy (or use the one named "rotation.gxy"
that came with this distribution), run it, and have the students observe
the results. When a significant amount of flattening is observable (note
that you will have to rotate your view of the galaxy to observe the flattening),
stop the simulation, and again have them write what they observed.
Discussion of the Simulation
Ask the students to discuss the differences between the two simulations.
Ask them if they can think of other situations in which rotation flattens
things. (Like hand-tossed pizza crust, spinning a Koosh® ball or key
ring, for example).
Discussion of Observation
Ask the students to look at what they wrote about the two simulations.
Tell them to suppose that they were the first people in the world to discover
that rotating galaxies flatten over time. Is what they wrote adequate to
explain this new discovery to the public or to other scientists? What would
they need to include in or change about their writing in order to make
it useful and clear to another person? Are they sure that they understand
the relationship? Should they do more or different tests? Have them critique
their own writing from this standpoint, and discuss what they learned from
this.
Assign them to write a clear and accurate report of what they observed.
Emphasize that it is important that they know what software was used, and
what parameters were set. Be sure to go through the setup procedure again
so that they can record this information.
Collaboration
After they have polished their reports, instruct them to prepare and post
a note to WebCaMILE for another group of students to see. If possible,
have the other group of students attempt to repeat the experiment as described
in the note, verify the findings of the first group, and provide feedback
about their methods and conclusions. Encourage both groups to ask questions
of each other's procedure and observations. If another group of students
is not available, you could split one class into two large groups and require
them to communicate only through writing.
Extensions
Further Experimentation
Have the students use GalaxSee to try different values for
the rotation, number of stars, dark matter, distributions, etc, observing
and recording the effects.
For example, have each student create a different galaxy, iterate it,
and record the experiment (including initial conditions). Then have the
students exchange reports with one another, and attempt to repeat each
others' experiments, comparing and reporting on the similarities or differences
of the results.
Thinking Harder
Ask the students how they would verify the conjecture that flattening in
galaxies may be a result of spinning. One way to do this is to see if the
flat galaxies we observe in nature are spinning (they are, and this is
observable with photometric tools attached to telescopes). However, not
all of the galaxies that we observe are flat. What would we expect to find
if we observed them to see if they were spinning? How might what we find
from these observations cause us to modify our conjecture?
Go to GalaxSee
Curriculum Resources
Shodor
Home Page
Last Update: May 13, 1996
Comments? Mail Michael South (msouth@shodor.org)
© 1996 Copyright The Shodor Education Foundation, Inc.