PASS
Planetarium Activities for Student Success
Activities from Volume 11: Astronomy of the Americas
Galileo Was Right!
Proving a sun centered solar system using a kinesthetic
model.
By Ken Brandt, M. Ed.
Astronomy Lecturer
UNCP Robeson Planetarium and
Science Center Director
JPL/NASA Solar System Educator, NASA Museum Alliance
partner
Here is a simple activity I whipped up based on a demo
I'm doing with my audiences this weekend as part of our
celebration of Venus and IYA. Let me know what you think.
This activity is useful for a quick, low cost method of
demonstrating one of Galileo's observations using his telescope:
the phases of Venus change, and Venus also appears to change
size as well. We will use orbital models of the moon and
Venus to demonstrate the following:
1. The moon's apparent diameter changes very little in
the course of one complete orbit of the earth.
2. If Venus orbited the Earth, we would likewise see very
little change in its apparent diameter.
3. As Venus orbits the Sun, its apparent diameter changes
greatly, and this change is consistent with a heliocentric
solar system.
Materials:
Ball about the size of a human head Tennis ball
or other ball of similar size
Stick lamp. Or other central single light source
Small ruler 10 foot (4 meter) tape measure
Open space (at least 30 feet, or 8 meters, in diameter)
Terms: Apparent diameter, Geocentric (earth centered),
Heliocentric (sun centered), Orbit (rotation), Model, Scale
Procedure: Arrange the stick lamp in the center of the
room. Make sure that it is the brightest single source of
light (draw window shades, or cover 'light leaks').
Arrange your students at the edge of the room.
Give each student a small ball. This ball represents
the moon. Students should hold the ball at arms length,
and slowly turn counter clockwise (to their left).
They should notice that the amount of light shining on
the moon appears to change from their viewpoint. These are
the phases of the moon, and you can use this as an opportunity
to defeat the misconception that the moon's phases are caused
by shadows, or by the moon shining using its own light.
Then have students measure the apparent diameter of the
moon at any 4 points in its orbit around their heads using
the ruler held 10 cm (3 inches) from the tip of their nose.
The students should observe a nearly constant diameter.
Point out that any object in a regular orbit around Earth
would show a similar pattern.
You will then move the students away from the edges of
the room, and have them cluster together closer to the lamp
(leave yourself at least 3 meters between them and the lamp).
Take the larger ball, and slowly walk around the students
at a distance of 3 meters away. Ask the students to make
observations of the ball. Try not to let your shadow fall
on the ball (holding it above your head will work nicely)
The students should notice that the ball is changing phase,
and remaining roughly the same apparent diameter. Students
then measure the apparent diameter of the larger ball at
4 points as you orbit around them, using the same ruler
held at the same distance from their nose. Tell them that
you have just demonstrated what Venus would look like to
Galileo if it orbited Earth.
Return the students to the edges of the room. Hold the
large ball, and walk around (orbit) the lamp at a distance
of 3 meters from it. Again, hold the ball aloft to keep
your shadow from interfering, and ask the students to observe
what is similar and different about the ball (point out
that this is the same ball you were just holding a few minutes
ago). They should observe that phases are similar, but the
ball appears larger when it's close and smaller when it's
far away. Then have them measure at 4 points in your orbit
of the sun with the ruler, using the same procedure as before.
They should include measurements when you are closest to
them, and again when you are furthest away from them. After
they have completed the measurements, ask them to draw what
Venus looked like when it was closest, and when it was furthest
away. Then, show them Galileo's drawings of Venus.
Ask them what motion Venus was doing when they drew it
(orbit of the lamp/Sun) And what motion Venus actually makes
in the sky (orbit the Sun).
Ask them if Galileo was right!
<You should point out that this model is way out of scale!
If the students' heads are the Earth, the moon would be
located about 25 feet (7 meters) away, instead of at arm's
length, Venus would be located at least 180 feet away, and
the Sun would be the size of the school building (about
55 meters wide) and located more than a mile away!>
Have fun with this!
Ken Brandt, M. Ed.
Director
Robeson Planetarium and Science Center , Lumberton,
NC
JPL/NASA Solar System Educator |