THE UNIVERSE IS A REALLY BIG PLACE

THE UNIVERSE IS A REALLY BIG PLACE
GOALS
■ Gain an intuitive feel for different measures of distance
■ Convert between various units of distance
■ Use scientific notation
■ Understand concepts of the astronomical unit and light-year
■ Create scale models of solar system and galaxy using a campus map
As we begin our study of life in the universe, you’ll find that our universe is indeed a really big place.
The distances between planets are unimaginably large, and the distance to the nearest star system is
even larger. The activities that follow ask you to carefully create several scale models and use them
to reason about the size and scale of the universe.
PART A: CONVERTING BETWEEN UNITS
1. Name a location that is about a 1-hour drive from your present location.
2. Approximately how far away (in miles) is the location you listed above?
Instead of miles, astrobiologists use a standard of measure that is used internationally, the kilometer
(km). Therefore, it will be useful for you to begin to think of distances in these terms.
Using your calculator, you can convert between miles and kilometers using the relationship that 1.609
kilometers = 1 mile. For example:
15.0 miles x 1.609 km = 24.1 km or about 24 km
1 mile
Note that we keep only three “significant” figures in the final answer. This is because there were only
three figures in the initial value 15.0 miles.
3. Calculate the number of kilometers for the distance you estimated in Question 2. Clearly show
all of your work as in the example calculation above.
4. Name a location that would take about 3 hours to drive to and estimate the number of kilometers
to that location.
5. Current estimates suggest that a liquid ocean may exist about 100 km beneath the icy surface of
Jupiter’s moon Europa. Give examples of two locations on Earth that are about 100 km apart.
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Activity 2
When dealing with very large numbers, you can easily enter them into your calculator using scientific
notation. Scientific notation is a kind of shorthand for large numbers used by scientists. There is a
special button on most scientific calculators that does this for you. For example, 93,000,000 is
typically written in scientific notation as 93 x 10 6 and can easily be entered into your calculator as 93
EXP 6 or possibly as 93 EE 6 or 93 EE X 6. In other words, the EXP or similar calculator key does the
X 10 operation for you.
6. For distances as large as the distance between planets, scientists frequently use a unit called the
astronomical unit, or AU. An AU is the average distance between Earth and the Sun (about 93
million miles). Calculate how many million kilometers there are in an AU.
7. If Jupiter is five times farther from the Sun than Earth is, how many AU are between Jupiter and
the Sun?
8. Venus orbits the Sun at a distance of 0.7 AU. Mars orbits the Sun at a distance of 1.5 AU.
Provide a sketch of the orbits of Venus and Mars that shows the relative distances of these
planets’ orbits around the Sun.
9. When Venus and Mars are closest to one another during their orbits around the Sun, how far
apart are they?
10. When Venus and Mars are farthest from one another during their orbits around the Sun, how far
apart are they?
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The Universe Is a Really Big Place
PART B: SCALE OF THE SOLAR SYSTEM
To better appreciate the unimaginable distances between objects in our solar system, it is useful to
construct a scale model that depicts these distances in a more familiar context. We will use scale
factors to convert the actual distances between objects within the solar system to a distance that
appropriately fits our scale model. A scale factor is simply “the desired size you would like for your
model” divided by the “actual size” of the thing being modeled.
scale factor = desired size
actual size
In this activity we will construct a scale model of our solar system to fit on a 100-yard football field.
The size of our solar system is roughly equivalent to the average distance between the Sun and Pluto,
about 40 AU. The scale factor for our football field-sized scale model will be:
scale factor = (actual distance between Sun & Pluto)
(desired size of scale model)
—
100 yards
40A U
scale factor —
100yards
40A U
scale factor = 2.5 yards per AU or 2.5 yards/Au
Then you will calculate the distance between the Sun and each of the planets using your scale factor.
For example, Mercury is 0.4 AU from the Sun. Therefore, the distance between the Sun and Mercury
on the football field would be:
Distance between Sun and Mercury = 0.4A U x 2.5 yards — 1 yard
AU
1. Determine an appropriate scale factor for a scale model of the solar system that will fit on to a
football field and record it below. Use the scale factor of 2.5 Yards/AU The first one has been filled in
for you.

Pluto may or may not formally be defined as a planet at this moment.
Life in the Universe — Activities Manual, 2nd Edition Prather, Offerdahl, and Slater
Activity 2
0 yds 50 yds 0 yds
2. Place labels clearly showing where each planet should be placed on the sketch of a football
field above.
3. Although Mars is farther from the Sun than Earth, Mars is often called an inner planet. Why
do you think Mars is called an inner planet?
4. How do the spacings of the inner planets compare to the spacings of the outer planets?
5. The farthest astronauts have traveled is to the Moon, which is located about 0.003 AU from
Earth and represents a 3-day journey one-way. Calculate the number of yards (using your
scale factor) between Earth and the Moon.
6. Is it possible to show the Moon’s orbit around Earth on your football field scale model
diagram? Why or why not?
7. If it takes 8 years for a spacecraft to travel from Earth to Jupiter, estimate the minimum time
it would take to travel from Earth to Saturn. Explain how you arrived at your estimate.
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The Universe Is a Really Big Place
PART C: PROPOSING A SCALE MODEL OF THE SOLAR SYSTEM ON YOUR
CAMPUS
In this activity, your group will develop a proposal for a scale model of the solar system on your
campus (Note: You may wish to choose an alternative nearby location such as a shopping mall or
downtown area rather than your campus for your scale model if desired.)
1. Use a copy of a campus map or a rough sketch on a separate piece of paper to locate
distinguishable campus landmarks. Pick two campus locations to place your scale model
between. Clearly indicate where you want to place the Sun and Pluto.
2. What is the distance between the Sun and Pluto on your map or sketch?
3. Using the distance in Question 2 as the desired size of your scale model, calculate the scale factor
(as you did in Part B) that you will use for your campus scale model of the solar system.
4. Complete the table below using your scale factor. Then clearly label the approximate position of
the Sun and the planets on your map or sketch.
PLANET
APPROXIMATE
DISTANCE FROM
SUN (IN AU)
APPROXIMATE PLACEMENT ON SKETCH (NEAR
WHAT OBJECT) AND DISTANCE FROM SUN IN
APPROPRIATELY SCALED UNITS

* Pluto may or may not formally be defined as a planet a this moment.
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Activity 2
5. Determine the appropriate distances to each of the following objects on your scale model and
label them on your map or sketch (if possible):
a. Moon’s orbit at 0.003 AU from Earth
b. Asteroid Ceres 2.8 AU from the Sun
c. Comet Halley at 18 AU from the Sun
d. Voyager space probe at 84 AU from the Sun
6. Alpha Centauri is the closest star system to the Sun at 272,000 (2.72 x 10 5) AU.
a. Calculate the distance to Alpha Centauri for your campus scale model. Show your work.
b. If you were to put this on your scale model, would it be on your campus, within your city
limits, in your state, on your continent, or anywhere on Earth?
7. The Sun is located 2 X 10 9 AU from the center of the Milky Way Galaxy.
a. Calculate the distance to the center of the Milky Way Galaxy for your campus scale model.
Show your work.
b. If you were to put this on your scale model, would it be on your campus, within your city
limits, in your state, on your continent, or anywhere on Earth?
8. The Andromeda Galaxy is the largest galaxy closest to our own at 164 x 10 9 AU.
a. Calculate the distance to the Andromeda Galaxy for your campus scale model. Show
your work.
b. If you were to put this on your scale model, would it be on your campus, within your city
limits, in your state, on your continent, or anywhere on Earth?
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The Universe Is a Really Big Place
PART D: SCALE OF THE UNIVERSE
In everyday language, we often use time as a way to describe distance. For example, one might say
that it is about a 6-hour flight from San Francisco to New York City or that it is a 3-hour train ride
from New York to Washington, D.C.
1. In units of time, estimate how long it is from where you are right now to the nearest state capitol
using:
a. a bicycle
b. a car
c. an airplane
For distances between different stars (interstellar distances) and between large collections of stars
called galaxies (intergalactic distances), scientists use a standard unit of distance called a light–year,
which is the distance light travels in one year. One light-year, abbreviated ly, is about 63,216 AU.
2. Imagine you are driving down a highway and see a billboard advertisement that reads, “This new
computer technology is light-years ahead of its time.” What is incorrect about the usage of lightyears in this sentence?
3. Calculate how many light-years away Alpha Centauri is from Earth. (Flint: Consider how many
AU Alpha Centauri is from Earth, Part C, Question 6.)
4. If you could travel in a spaceship at the speed of light, 300,000 kilometers per second (km/sec),
approximately how many years would it take you to travel from Earth to the next star system,
Alpha Centauri? (You don’t really need a calculator for this calculation.)
5. Would the time you estimated in Question 3 be significantly different if you traveled from the
Sun to Alpha Centauri instead of from Earth? Explain your reasoning.
6. Our home galaxy, the Milky Way Galaxy, has a diameter of about 100,000 light-years. If Earth
is about halfway out from the center of our Milky Way, about how many light-years is Earth
from the center?
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Activity 2
7. The Andromeda Galaxy is located about 2.6 million light-years away from the Milky Way. How
many times greater is the distance between the Milky Way and Andromeda compared to the
distance between Earth and the center of the Milky Way?
8. The most distant galaxies known are about 10 billion light-years away. How many times farther
away is the most distant galaxy compared to the distance to the Andromeda Galaxy?
9. Put the following objects in order from closest to- Earth to farthest from Earth.
a. Andromeda Galaxy
b. The Sun
c. Most distant galaxies
d. Alpha Centauri
e. Pluto
f. The center of the Milky Way Galaxy
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