phases of moon, earth-sun system
I have attempted to teach these things in a 100-level, non-science student
class.
Moon Phases:
For the moon I use a white volleyball, a globe and an old projector
that gives me collimated white light.
Have students cluster near "Earth" and observe.
Hold the projector in front of class, lighting the Earth. Ask
the students which side of the "Earth" is the dark side. Have them
move there for "lunar observations."
Have a student hold the volleyball between "Earth" and "moon," and
at the various positions in an orbit around "Earth."
One can see the phases of the moon on the volleyball. (You may
need to swing the projector/sun out to each side of the front of the classroom
as the moon goes through its orbit, so that the "sun" is shining normally
on the moon.
Sun-Earth:
I stole ideas from Project Star. Purchase and distribute clear,
acrylic hemispherical domes that one can buy at art supply shops cheaply.
Also distribute a piece of paper with the outline of the dome on it, a
center point, and a North arrow.
Have students take both of these things, a pen and a compass outside
several times during a day when the sun is clearly observable. They
should hold the pen so that the (sun's) shadow of the tip falls on the
center of the hemispherical dome, and mark where the tip is on the half-dome.
Date and time stamp each observation. Take several on the same day.
Take observations for a day twice or more, spaced several weeks or months
apart. Use different colored pens for different days.
This represents a set of observations. I have students
bring these to class/lab on a specified day. We start using the Ptolemaiic
model (spelling?). Tape an unmarked dome over where you are on a
globe (centered over your city or region). Have a student hold the
globe with dome. Start with the sun (a laser pointer) in the center
and have the Earth orbit the sun.
Make model-derived data by marking where the laser pointer light hits
the unmarked dome on the globe. This is made easier as the laser
light will reflect directly back at the "sun" (laser pen holder)
when the light is aimed directly at the (local) normal to the dome.
Have a student mark where the laser pointer hits the dome for several
positions of the sun in its orbit around the Earth.
Compare the real observations to the synthetic ones. Are they
consistent with each other (yes, for one day only).
Now ask how one can generate seasonal variations in the Sun's elevation
vs. azimuth using the Earth-centric model (they have observations on their
domes which demand this change).
Finally, I put the sun the center, hold the globe in one position (hit
seasons while you're there since the Earth is tilted) and make synthetic
data for one day. It matches observations for one day. Try
another day. See if students can figure out where the Earth needs
to be relative to the sun for the days of their observations.
That's it. I have a write-up if anyone is interested. The
main point here is that many students have difficulty seeing balls representing
the Earth, moon and sun in their minds. "Geometric thinking" (for
lack of a better phrase) is not well-developed in many students.
These exercises are meant as a concrete model to encourage this type of
thinking. I hope to get an article in TPT soon about this.
Cheers,
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