BACKGROUND:
The planets move around the Sun. This motion is called
revolution. Each of the planets also spins around an internal axis
which is called rotation. Although these are simple concepts, our
language sometimes uses these words differently. For example, revolving
sometime is used to mean an object turning on itself, like a revolving door;
this is actually rotation. This makes the astronomical use of these terms
confusing for students.
PROCEDURE:
- Explain the astronomical meaning of revolve and rotate to the
students. Darken the classroom. Have 4 students stand back to back and
shine the flashlights outwards. These students are the "Sun".
Divide the remaining students so they slowly revolve around the
"Sun". They are "planets". Have the
"planets" rotate by spinning as they revolve around the Sun.
Make sure you do this activity in a large open space.
Ask the "Sun" how long it takes the planets to complete one
revolution. Ask them how long one revolution of the Earth takes (365
days or one year). Ask the "planets how long it takes them to
rotate. Also ask them how long it takes the real Earth to rotate (1 day)
- Have a pair of students pretend to be the Earth and the Moon. Have the
"Earth" stand still and rotate, and the "Moon"
revolves around the Earth. Explain to the class that these two motions
happen as the entire Earth-Moon system revolves around the Sun.
- Ask the class if the Earth and Moon "shine" by themselves
(no). Ask the students where the light comes from (the Sun). State that
the light starts from the Sun, bounces off (is reflected) from the Moon
and then we see it on Earth. It may look like the Moon has its own
light, but it does not.
- Using the inflatable globes, show students that the Earth does not
rotate straight up and down, but that its rotational axis is tilted at
an angle away from the Sun. The actual tilt averages about 23.50.
Designate a spot in a clear part of the classroom as the Sun. Tell the
students that when you say "revolution" they should start
walking around the Sun. When you say "rotation", they should
start to turn around on their axes. This can be a fun game. Continue
until the students get it right. This may take a while!
- As the students are rotating on their axes, make sure they realize
that when they are facing the flashlights (the Sun) it is day, and when
they are facing away it is night.
- Make sure that your students understand that rotation and revolution
are going on at the same time. Some students may have difficulty doing
both activities simultaneously. You may wish to have a student with good
motor skills demonstrate them to the class. Tell the students that
everything in the Universe is moving: the Earth, the Moon, the planets,
the Sun, and even entire galaxies. The one thing all the parts of the
Universe have in common is that they are moving. Your students are
moving with the Earth as you talk!
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