Planets and Relative Size
By
April Garner
OBJECTIVES:
Students will calculate the radii for scale models of the planets.
Students will compare the relative sizes of the planets.
Students will make a scale model of each planet.
RELATION
TO MISSOURI FRAMEWORKS:
5-8: VA2 Celestial objects possess both similarities and differences.
5-8: IV3 Mathematics is used in the real world.
5-8: IV2 Mathematics is used in other subject areas.
CONTEXT:
Grade Level: 5-6
Group of 15-20 for StarLab presentation
PREREQUISITE:
Students will have some knowledge of scale and relative size from the
previous lesson and will have some knowledge of the sun and the nine planets in
our solar system.
In a previous lesson, students will have also drawn circles using a
ruler, a compass, and the circle’s radius.
MATERIALS:
Balls of different sizes
StarLab Portable Planetarium
Planet Cylinder
Arrow pointers
Red flashlight
Cardboard squares (18”x 18”)
Compass, drawing
Black marker
Black construction paper (18”x 20”)
Blue construction paper (2’’ squares)
Metric ruler
Scissors
Masking tape
PROCEDURE:
1.
Review the concept of relative size by
showing balls of various sizes. Discuss
the size of each ball relative to the size of the others. Ask: How would
the Sun and planets compare with one another?
[Answers will vary.]
2.
Review the concept of scale and why
scaled drawings are useful. Remind
students that scaled drawings allow us to visualize the relative sizes of actual
objects. Ask: How can we visualize the relative size of the planets?
[Make scaled drawings of the planets and place them next to each other to
compare.]
3.
Ask:
What shape would you use to make a scale drawing of the planets?
[A circle] What measurement
would you need to make a scaled model? [The
diameter or the radius of the circle]
4.
Explain to students that in this lesson
they are going to observe and make scaled drawings of the planets.
5.
Review the planets in their order.
Write the planets and the actual size of the planets on the board.
Ask: Can you make the models
of these planets their actual size? [No.
The planets are too big.]
6.
Explain that when you want to visualize
the planets’ sizes, the planets’ models can be made to scale.
Ask: When you draw the
planets to scale can you use different scales for each model of the planets to
show relative size? [No.
In order to show relative size accurately, the same scale must be used
for all the planets.]
7.
Tell the students that the scale for
the models on the board is 1 cm to 5,000 km.
Above the planets on the board, write 1 cm: 5,000 km. Pass out Activity Sheet 6.
Have the students look at the planets in the chart (skipping the sun in
that chart). Refer to the actual
diameters and the scaled diameters. Ask:
How would you calculate the radius of these models?
[Divide the diameters by 2]
8.
Have the students calculate all the
radii of the planets on Activity Sheet 6.
9.
After the children have finished, write
all the scaled radii on the board next to the respective planet.
Together as a class calculate the scale diameter and radius of the sun.
[Divide 1,392,000 by 5,000 to get the diameter and then divide the
diameter by 2 to get the radius.]
10.
Give the children a moment to answer
the question at the top of Activity Sheet 6 and then review the answer.
[Reduce the actual diameter of the planets according to the same ratio,
draw circles using the scaled radii, and compare the size of the circle.]
11.
Inform the students that at this time
they will enter the StarLab in order to compare the relative size of the
planets. Review the rules for the
StarLab before entering.
12.
After the students are seated, turn on
the planet cylinder and let it begin to rotate.
13.
Explain to the students that the
planets they see have been made to scale.
Use the pointer to identify the planets and their names. Inform them to take a moment to look at the planets and
compare their sizes with each other and the sun.
14.
As the planets rotate ask the following
questions:
a.
Judging from the models, which planet
is larger than Saturn? [Jupiter]
b.
By looking at these scaled models, what
do you notice about the relative sizes of the planets? [Answers will vary. The
students may discuss how small Earth is, how much larger Jupiter and Saturn are,
or how tiny Pluto is.]
c.
Stop the rotation at Jupiter and
Saturn. Point out the actual
diameters of these planets. What do
the measurements tell you about the relative sizes of the actual planets? [Jupiter is larger than Saturn]
d.
If you looked at just the actual
diameter measurements of the planets, what could you tell about the relative
sizes of these planets? [You can
tell the planets are different sizes.]
e.
If you can tell the planets are
different sizes just by looking at the diameter measurements, why would you need
a scale model? [Answers will vary.
Students should understand that actually seeing scaled models gives a
clearer mental picture of the vast differences in sizes.]
15.
Inform students that at this time they
will be carefully exiting the StarLab and returning to class. In the classroom they will make scaled models of the planets.
16.
In the classroom, divide the students
into teams of two.
17.
Distribute the rulers, scissors,
compasses, cardboard squares, blue construction paper squares, black
construction paper, and black markers. Have
the roll of masking tape available.
18.
Students will use the scale on Activity
Sheet 6. They will make Earth from
the blue construction paper and the other planets will be on the black
construction paper. [You may want
to suggest to the students to draw the larger planets first, start near the
corners of the black paper.]
19.
Remind the that to make a model of a
planet they need to place the construction paper on the cardboard, measure the
radius of the planet on the metric ruler, set the compass at that radius, draw
the circle on the paper, and cut the paper out.
[The scaled radii of Mercury, Venus, Mars, Pluto, and Earth are too small
for the compass. Therefore, the
students will measure the scaled diameters of these five planets with
their rulers and hand-draw the circles.]
20.
The students should label the planets
according to the instructions on Activity Sheet 6.
21.
After the students have finished making
their models, they can arrange them in order from the Sun and compare the sizes
once again.
RESOURCES:
Carpenter, Debbie, etal. Solar
System, DSMII.
1996. Delta Education, Inc.
Hudson, NH.
http://www.exploratorium.edu/ronh/solar_system/
http://www.erwin-purucker.de/solarsy.htm
EXTENSIONS
AND/OR ADAPTATIONS:
After the students have finished theirs models, assign the students to
make a display of their models in an orbit around the Sun.
In the display, they could add moons and the asteroid belt.
CONTENT
BACKGROUND:
It is hard to imagine the enormity of the objects that
make up the Solar System. The
largest object in our Solar System is the Sun, and its diameter is 1,392,000 km.
The smallest planet in our Solar System is Pluto with a diameter of 2,400
km. To create a model of our Solar
System for students to visualize relative sizes of the Sun and the planets
requires the use of a scale.
The comparison of the numerical measurements of the planets’ diameters
does tell the planets relative size. However,
a visual representation gives a clearer image of the size of the planets. Students may understand that Jupiter is larger than Pluto,
but they will be amazed at the difference when they compare the visual pictures
or models of these two planets.
APPENDIX: