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How are astronomical distances measured?
Description:
Students will create a scale model of the solar system using astronomical units.
California State Standard(s): SC.8.4.c. Students know how to use astronomical units and light years as
measures of distances between the Sun, stars, and Earth.
Student Materials (per group)
 Strips of paper
 Planets
 Scissors
 Tape or glue
 Calculator
 Meter stick
Additional Teacher Materials:

Background and Misconceptions:
Since the distances are vast in the solar system and between stars, astronomers have created various units to
represent these large distances. They use them only because they are easier to use and they are agreed upon
quantities. The common units are:


Astronomical unit (AU) – This is the average distance between the earth and the sun. 1 AU is equal to
approximately 93,000,000 miles or 150,000,000 kilometers.
Light year (LY) – this is the distance that light travels in 1 year. It is equivalent to about 6 trillion miles
or 63,241.1 AU’s.
Other units are used by astronomers when necessary or convenient. For example, an additional dimension is the
parsec, with is about 3.3 light years. Although a parsec is not significantly different from a light year, its origin
resulted from the shifting of stars apparent positions in the night sky during the course of earth’s orbit around
the sun. A star that shifts it’s position by 1 arcsecond (which is 1/60th of an arcminute or 1/3600th of a degree.)
is said to be 1 parsec from earth with the difference in earth’s position in its orbit is 1 AU.
Teacher Guided Questions to Inquiry: Use these questions to get the students started on their own inquiry!
1. How are vast distances in the solar system and galaxy measured?
2. What are astronomical units and light years?
3. How can we scale the solar system and how far away are even the closest stars?
Additional Hints:


Use adding machine tape for the strips of paper.
Students may wish to color the planets prior to gluing or taping onto the paper.
TEACHER ANSWER KEY
Description: Common units of measurement such as centimeters, meters, and miles are often too small to use
when measuring the vast distances between objects in space. Astronomers have created other units to use to
measure distances between the sun, planets and the stars.
In this activity, you will create a scale model of the solar system using a common unit of measurement in
astronomy.
Materials:
Strips of paper
Scissors
Planets
Calculator
Tape or glue
Meter stick
Procedures:
1. Astronomical units are used to measure to measure large distances within the solar system. An astronomical
unit is equal to the average distance between the earth and the sun. This is also equal to 93,000,000 miles.
On the table below, determine the distance, in astronomical units (AU) for each of the planets.
2. Create a model of the distances of the planets. Multiply the value in AU’s by 10 (AU x 10 cm). This value
will be used to determine where to place the planet on the strip of paper. At one end, glue or tape the planet.
3. On the strip measure the distance from the SURFACE of the sun to the CENTER of the planet.
Planet
Astronomical Units
Distance on tape
Mercury
Distance from Earth to
the Sun
(miles)
37,200,000
(1 AU = 93,000,000)
0.4 AU
(1 AU = 10 cm)
4 cm
Venus
65,100,000
0.7 AU
7 cm
Earth
93,000,000
1.00 AU
10 cm
Mars
139,000,000
1.5 AU
15 cm
Jupiter
483,600,000
5.2 AU
52 cm
Saturn
883,500,000
9.5 AU
95 cm
Uranus
1,785,600,000
19.2 AU
192 cm
Neptune
2,799,300,000
30.1 AU
301 cm
Questions:
1. While astronomical units are used to measure the distances within the solar system, it is not easy to use them
to measure the distances to the stars. The nearest star is Proxima Centuari. It is 4.3 light years away. A
light year is equal to 63,241.1 AU’s.
a. How far way is Proxima Centauri in Astronomical Units?
271,937 AU
b. How many centimeters down your paper strip would the star be located?
2,719,370 cm, or 27,193.7 kilometers or 16,897 miles!
c. Where would this be at the scale of the paper? (Inside the room? School? City?)
This would be far outside your city, and in fact would be 2/3rds of the way around the earth!
2. A light year is the distance that light travels in one year. If you turned on a flashlight, at the end of 1 year,
the beam of light will have traveled about 6 TRILLION miles (6,000,000,000,000). Why do astronomers
use units such at light years or astronomical units to measure distances?
Since the distances are vast, it is easier to use units that represent larger values. 1 light year is easier to
express than 6 trillion miles. Different units are used only because they are easier to use!
How are astronomical distances measured?
Name _____________________________
Date ____________________
Description: Common units of measurement such as centimeters, meters, and miles are often too small to use
when measuring the vast distances between objects in space. Astronomers have created other units to use to
measure distances between the sun, planets and the stars.
In this activity, you will create a scale model of the solar system using a common unit of measurement in
astronomy.
Materials:
Strips of paper
Scissors
Planets
Calculator
Tape or glue
Meter stick
Procedures:
1. Astronomical units are used to measure to measure large distances within the solar system. An astronomical
unit is equal to the average distance between the earth and the sun. This is also equal to 93,000,000 miles.
On the table below, determine the distance, in astronomical units (AU) for each of the planets.
2. Create a model of the distances of the planets. Multiply the value in AU’s by 10 (AU x 10 cm). This value
will be used to determine where to place the planet on the strip of paper. At one end, glue or tape the planet.
3. On the strip measure the distance from the SURFACE of the sun to the CENTER of the planet.
Planet
Mercury
Distance from Earth to
the Sun
(miles)
37,200,000
Venus
65,100,000
Earth
93,000,000
Mars
139,000,000
Jupiter
483,600,000
Saturn
883,500,000
Uranus
1,785,600,000
Neptune
2,799,300,000
Astronomical Units
Distance on tape
(1 AU = 93,000,000)
(1 AU = 10 cm)
1.00 AU
10 cm
Questions:
1. While astronomical units are used to measure the distances within the solar system, it is not easy to use them
to measure the distances to the stars. The nearest star is Proxima Centuari. It is 4.3 light years away. A
light year is equal to 63,241.1 AU’s.
a. How far way is Proxima Centauri in Astronomical Units?
b. How many centimeters down your paper strip would the star be located?
c. Where would this be at the scale of the paper? (Inside the room? School? City?)
2. A light year is the distance that light travels in one year. If you turned on a flashlight, at the end of 1 year,
the beam of light will have traveled about 6 TRILLION miles (6,000,000,000,000). Why do astronomers
use units such at light years or astronomical units to measure distances?