Size and Scale of the Universe (Teacher Guide)
Overview:
The Universe is very, very big. But just how big it is and how we fit into the grand scheme can
be quite difficult for a person to grasp. The distances and sizes are so far beyond our everyday
experience.
Many activities have been created to help gain a sense of the scale of the Solar System by
building scale models of it. Activities for scale models of the entire Universe are lacking,
however, because of the sheer size of it. One cannot reasonably create a scale model of the
Universe that includes all of its components—from people to superclusters—and
simultaneously scales their distances and sizes.
This activity attempts to overcome that difficulty by examining the Universe at different realms.
First, we start with Earth and zoom out to the Sun and then the Solar System. We continue
zooming out from the Solar System, to galaxies, all the way out to the observable Universe.
Each step of the way, we use the room we are in to represent a realm of the Universe and then
look for common materials that can represent the astronomical objects within each realm, all
to scale.
Grade Level:
This lesson is intended for grades 8-12, but can be adapted down for lower grade levels as well.
Standards Correlation: See Appendix A for California, Texas, NSES, and AAAS alignment
Objectives:
• To learn about the structures of the various realms of the Universe
• To gain a sense of relative scales of the various realms of the Universe
• (Optional) To learn the various methods astronomers use to determine distances
Time:
Between 60-120 minutes:
• 60 minute option: you can speed through everything in 60 minutes by not having the
students write anything down (no student worksheets), skimming over the new
concepts and vocabulary, and not showing slides 16-22 (this approach is best if you are
solely looking for the immediate “WOW!” effect)
• 120 minute option: this is recommended for most classes because it allows time for the
students to digest and synthesize the new concepts and vocabulary. Experience shows
that students are highly engaged with this topic and typically want more time to ask
questions and let the concepts “sink in”. The mid-way break point typically occurs
several slides into the ‘Explore and Explain’ section (somewhere around slide #10 ‘The
Solar Neighborhood’).
Materials:
For the whole class:
 Accompanying Powerpoint (or PDF)
presentation titled ‘Size and Scale of
the Universe’
 Projector and screen for showing
the Powerpoint
 A Globe (optional)
For each group of students:
 Grains of salt (<0.5mm diameter)
 Peppercorn or small bead or BB
(~5mm diameter)
 Small Button (~8mm diameter)
 Large Button (~1.25 cm diameter)
 Grapefruit or Wiffle Ball (~9cm)
 CD or Roll of Masking Tape or Large
Cookie (~10 to~12cm diameter)
 Small paper plate (~15cm diameter)
 Large Pizza Box or Circular Piece of
Paper (~50cm in diameter)
 Anything else that is approximately
the same size as any of these objects
Grading:
Please refer the ‘Evaluate’ section at the end of this Teacher Guide
Getting Ready:
Gather the materials listed above and separate them into piles for each group (1-4 students per
group). Each pile should contain one or more of each of the objects listed (feel free to use
objects that are not listed here, especially if they are the appropriate sizes).
Ideally this activity should be conducted in a room that is approximately 10 meters by 10
meters, but it is definitely not crucial. The activity involves students imagining that the room
they are in represents a certain realm (e.g. Solar System, Galaxy, Supercluster, etc..) and then
guessing the relative size of the smaller realms inside of it. The instructions and answers
provided in these instructions assume that the room is 10m x 10m. If you do not have access to
a room of this size there are two options:
1) (recommended) Mention to the students that they should assume (envision) a room
that is 10m x 10m. Give them something to reference that is approximately 10 meters
long (the short end of a doubles tennis court is 11m, the average school bus is about
11m). Remind them throughout the activity that the answers are for a 10m x 10m room.
2) Use the accompanying excel file to calculate the answers (and object sizes) based on
your actual room size. Note: this will also change the objects and materials that you will
need to provide as the ‘answers’).
Procedure:
Engage:
Begin with a globe, and point out the location of the classroom allowing students to gain
some sense of the size of Earth in relation to the places they are familiar with (e.g., it
takes five hours to fly 3,000 miles, or forty hours to circle the Earth).
1) Show slide #2: ‘What is your cosmic address?’
Tell the students: “Suppose you had an alien friend who lived across the universe,
billions of light years away. And suppose they wanted to mail you a letter through
some sort of intergalactic postman. What address would you give them?”
Have the students brainstorm with their neighbor what their “mailing address” in
the Universe is. The “mailing address” should contain one line for each realm and
should start small and move out, beginning with:
• Street
• City
• State
• Country
• Continent
• Hemisphere
• Planet
…but then the students should keep going further out and brainstorm what
other lines (realms) should be added (e.g. third planet from the Sun, Solar
System, Spiral Arm, Milky Way Galaxy, Galaxy Cluster, etc..)
Request responses from students and write them on the board (or type them into
the powerpoint) until all are listed.
2) Show slide #3: (table with ‘Realm’ and ‘Guesses’ on top)
Explain that there are many different ways to divide up the realms of the Universe,
but that most astronomers typically think in terms of the ones listed here in the left
column. Mention that these realms will be defined and explained in more detail later
into the activity.
3) Distribute the materials to each group. Point out that they are provided as scale
models to represent relative sizes.
4) Tell students that the smallest object – the grain of salt – will be our model of the
Earth.
5) Now that they know the size of the Earth, ask students to work with their neighbor
to figure out which objects could represent each realm of the Universe going out
(i.e., each subsequent line on the “mailing address”). Have them refer to the realms
listed on the powerpoint slide (#3). Point out that they are not constrained by the
objects provided to them. They can suggest larger objects or larger examples if
they think it is necessary.
6) Ask the students what object (or larger example) they chose to represent each
realm. Write their answers on the board (or type them into the powerpoint). Review
their guesses and ask for their reasoning. Laugh condescendingly at their puny
guesses.
7) Show slide #4 (table that is filled in - with ‘Realm’, ‘Actual Size’… on top)
Give them time to absorb what is being shown, explain that the last column has the
correct answers to the previous challenge. If time allows, reveal each row one by
one.
8) Show slide #5: Realms of the Universe and continue to the next section.
Explore and Explain:
Pass out the Student Activity
Worksheets (one per student).
1. Sun and Earth:
• Show Slide #6: Earth -Discuss the
talking points on the side.
• Show Slide #7: Sun -Discuss the
talking points on the side.
• Show Slide #8: Sun & Earth -Discuss
talking points on the side.
Ask the students to imagine that
the Sun is the size of the classroom,
and then have them hold up an
object representing how large Earth
would be.
*Note: Remind the students to assume a
large classroom (10 meters square – or
10 meters in diameter):
Page 1 of 4 of the Student Worksheet
(a) How large would the Earth be?
1a) Answer: A grapefruit or Wiffle Ball (9.14 cm diameter)
Have the students show their math on their worksheets for Question I (they can/should use a
calculator).
2. Solar System:
• Show Slide #9: The Solar System
-Discuss talking points on the side.
Ask the students to now imagine
that the Solar System out to the
boundary between the Solar Wind
and interstellar space (200 AU
diameter) is the size of the
classroom.
(a) How large would the Sun be?
2a) Answer: A grain of salt (0.46
mm diameter)
(b) How large would Earth’s orbit around it
be?
2b) Answer: A CD, or a bit
smaller like a roll of masking
tape (10 cm diameter)
(c) How big would Earth be?
2c) Answer: Microscopic bacteria
(4 microns [4 x 10-6
meters])
Give the students time to answer Question II (“What is an AU?”). The answer is on slide #8 ‘Earth &
Sun’(and at the end of this teacher guide).
Page 2 of 4 of the Student Worksheet
3. Solar Neighborhood:
• Show Slide #10: The Solar Neighborhood -Discuss talking points on the side.
Ask the students to zoom out and now imagine that the Sun’s Neighborhood (40 light-year
diameter) is the size of the classroom.
(a) How large would the Solar System be?
3a) Answer: A grain of salt (0.8 mm diameter)
Give the students time to answer Question III (“What is a light-year?”). The answer is on the current
slide #10 ‘The Solar Neighborhood’ (and at the end of this teacher guide).
4. Milky Way:
• Show Slide #11: The Milky Way
Galaxy -Discuss talking points on
the side.
Ask the students to zoom out and
now imagine that the Milky Way
Galaxy (100,000 light-years
diameter) is the size of the
classroom.
(a) How large would the Solar
Neighborhood be?
4a) Answer: A peppercorn or
bead (4 mm diameter)
5. Local Group:
• Show Slide #12: The Local Group
-Discuss talking points on the side.
Page 3 of 4 of the Student Worksheet
Ask the students to zoom out and now imagine that the Local Group of galaxies (6.5 Million
light-years diameter) is the size of the classroom.
(a) How large would the Milky Way be?
5a) Answer: A small paper plate (15.4 cm diameter)
Have the students show their math on their worksheets for Question IV (they can/should use a
calculator).
6. Local Supercluster:
• Show Slide #13: The Local Supercluster -Discuss talking points on the side.
Ask the students to zoom out and now imagine that the Local Supercluster of galaxies (130
Million light-years diameter) is the size of the classroom.
(a) How large is the Local Group?
6a) Answer: An extra-large pizza
(50 cm diameter)
(b) How big is the Milky Way?
6b) Answer: A small button (8
mm diameter)
7. Universe:
• Show Slide #14: The Universe
-Discuss talking points on the side.
• Show Slide #15: The Universe
-Discuss talking points on the side.
Ask the students to zoom out and
now imagine that the entire visible
Universe (91 Billion light-years
diameter) is the size of the
classroom.
Page 4 of 4 of the Student Worksheet
(a) How big is the Local Supercluster?
7a) Answer: A large button (1.4 cm diameter)
(b) How big would the Local Group be?
7b) Answer: A grain of salt (0.7 mm diameter)
Elaborate: (optional)
Showing Slide #s 16-22 which cover how astronomers know and understand these distances.
o Show Slide #16: So How Do We Know These Distances?
o Show Slide #17: The Standard Rulers -Discuss talking points on the side.
o Show Slide #18: Parallax -Discuss talking points on the side.
o Show Slide #19: The Standard Candles -Discuss talking points on the side.
o Show Slide #20: Cepheid Variable Stars -Discuss talking points on the side.
o Show Slide #21: Supernovae (Type 1a) -Discuss talking points on the side.
o Show Slide #22: The Cosmic Ladder -Discuss talking points on the side.
Evaluate:
There are 5 boxes on the Student Worksheet where students are asked to answer questions as
they go through the activity – these are the questions that can be graded.
The other questions (about guessing which object represents each realm) are not meant to be
graded.
The recommended breakdown for weighting each question is:
• Question I = 15%
• Question II = 15%
• Question III = 15%
• Question IV = 15%
• Question V = 40%
Grading Rubric:
Question I = 15% (“Show your math to see if you get a similar answer”):
• Full credit (15%) - the student shows the proper mathematical steps to reach the
correct answer (0.0913669 meters or 9.14cm)
• Partial credit (10%) – the student shows the proper mathematical steps but reaches
the wrong answer
• Partial credit (5%) – the student shows the wrong mathematical steps and reaches
the correct answer
• No credit (0%) – the student shows the wrong mathematical steps and reaches the
wrong answer
Question II =15% (“What is an AU?”):
• Full credit (15%) – the student covers all 3 of the following main points:
1. Stands for Astronomical Unit
2. Is the average distance between the Earth and the Sun
3. Is about 150 kilometers (or 93 million miles)
• Partial credit (10%) – the student covers 2 of the 3 main points
• Partial credit (5%) – the student covers 1 of the 3 main points
• No credit (0%) – the student covers 0 of the 3 main points
Question III =15% (“What is a light-year?”):
• Full credit (15%) – the student covers all 3 of the following main points:
1. Is the distance that light travels in one year
2. Is about 10 trillion kilometers (or 63,000 AU)
3. The student does not refer to it as a unit of time
• Partial credit (10%) – the student covers 2 of the 3 main points
• Partial credit (5%) – the student covers 1 of the 3 main points
• No credit (0%) – the student covers 0 of the 3 main points
Question IV =15% (“Show your math to see if you get a similar answer”):
• Full credit (15%) - the student shows the proper mathematical steps to reach the
correct answer (0.1538461 meters or 15.4cm)
• Partial credit (10%) – the student shows the proper mathematical steps but reaches
the wrong answer
• Partial credit (5%) – the student shows the wrong mathematical steps and reaches
the correct answer
• No credit (0%) – the student shows the wrong mathematical steps and reaches the
wrong answer
Question V =40% (“Write one paragraph describing how your perspective and
understanding of the Universe have changed after participating in this activity”):
• (0-40%) Up to the teacher’s discretion to determine the level of thought and effort
put into answering the question.
Appendix A: Standards Correlation
California State Science Content Standards:
Grades 9-12: Earth Sciences, Earth’s Place in the Universe
1. Astronomy and planetary exploration reveal the solar system’s structure, scale, and change over time. As a basis for understanding this
concept:
d. Students know the evidence indicating that the planets are much closer to Earth than the stars are.
2. Earth-based and space-based astronomy reveal the structure, scale, and changes in stars, galaxies, and the universe over time. As a basis for
understanding this concept:
a. Students know the solar system is located in an outer edge of the Milky Way galaxy, which spans 100,000 light years.
b. Students know galaxies are made of billions of stars and comprise most of the visible mass of the universe.
Grade 8: Earth in the Solar System (Earth Sciences)
4. The structure and composition of the universe can be learned from studying stars and galaxies and their evolution. As a basis for
understanding this concept:
a. Students know galaxies are clusters of billions of stars and may have different shapes.
b. Students know the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature, and color.
c. Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth.
Texas Essential Knowledge and Skills (TEKS):
Grade 9-12 Astronomy Course:
112.33(c)-6: Science concepts. The student knows our place in space. The student is expected to:
(A) compare and contrast the scale, size, and distance of the Sun, Earth, and Moon system using data and modeling.
(B) compare and contrast the scale, size, and distance of objects in the solar system such as the Sun and planets using data and modeling.
(C) examine the scale, size, and distance of the stars, Milky Way, and other galaxies through the use of data and modeling.
(D) relate apparent versus absolute magnitude to the distances of celestial objects.
(E) demonstrate the use of units of measurement in astronomy, including Astronomical Units and light years.
112.33(c)-12: Science concepts. The student knows the variety and properties of galaxies. The student is expected to:
(B) recognize the type, structure, and components of our Milky Way galaxy and location of our solar system within it.
Grade 8 Science:
112.20(b)-8: Earth and space: The student knows characteristics of the universe. The student is expected to:
(A) describe components of the universe, including stars, nebulae, and galaxies, and use models such as the Herztsprung-Russell diagram for
classification.
(B) recognize that the Sun is a medium-sized star near the edge of a disc-shaped galaxy of stars and that the Sun is many thousands of times
closer to Earth than any other star.
(D) model and describe how light years are used to measure distances and sizes in the universe.
National Science Education Standards (NSES):
Grades 9-12: Earth and Space Science (Content Standard D):
The Origin and Evolution of the Universe
Early in the history of the universe, matter, primarily the light atoms hydrogen and helium, clumped together by gravitational attraction to form
countless trillions of stars. Billions of galaxies, each of which is a gravitationally bound cluster of billions of stars, now form most of the visible
mass in the universe.
Grades 5-8: Earth and Space Science (Content Standard D):
Earth in the Solar System
The earth is the third planet from the sun in a system that includes the moon, the sun, eight other planets and their moons, and smaller objects,
such as asteroids and comets. The sun, an average star, is the central and largest body in the solar system.
AAAS Benchmarks for Science Literacy:
Grades 6-8: 4. The Physical Setting, A. The Universe:
-The sun is a medium-sized star located near the edge of a disc-shaped galaxy of stars, part of which can be seen as a glowing band of light that
spans the sky on a very clear night. 4A/M1a
-The universe contains many billions of galaxies, and each galaxy contains many billions of stars. To the naked eye, even the closest of these
galaxies is no more than a dim, fuzzy spot. 4A/M1bc
-The sun is many thousands of times closer to the earth than any other star. Light from the sun takes a few minutes to reach the earth, but light
from the next nearest star takes a few years to arrive. The trip to that star would take the fastest rocket thousands of years. 4A/M2abc
-Some distant galaxies are so far away that their light takes several billion years to reach the earth. People on earth, therefore, see them as they
were that long ago in the past. 4A/M2de