Student Answer Sheet
The Expanding Universe
Overview
In this activity, you will
use Hubble Space Telescope Images to view how objects in the Universe change
and create scientific models of the Universe.
Materials
and Technology Required
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Exploration
Below is a graph that is used
by astronomers. Can you figure out what it represents? 
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| What do the values on the
horizontal axis represent?
How might scientists measure this value? |
What do the values on the horizontal
axis represent?
How might scientists measure this? |
| What do the values on the
vertical axis represent?
How might scientists measure this value? |
What do the values on the vertical
axis represent?
How might scientists measure this? |
| Which do you think is harder to measure? | Which do you think is harder to
measure?
Which do you think is harder to measure? |
| What are the units of the
"slope"?
What could slope represent? What about its inverse? |
What are the units of the "slope"?
What could slop represent? What about its inverse? |
Concept Introduction
The universe has 4 dimensions: height, width, depth, and time. They are bound together as space-time. As the universe expands, the view from any one place in the universe remains the same. It is homogeneous and appears linear in its progression. The Hubble Law states that the recessional velocity of a galaxy is proportional to its distance from us. The velocity of the moving body is measured using the Doppler effect. The distance is more difficult to measure. It is measured by its apparent angular size.
Instructions
1. In this activity, you are going to create a model of the expanding Universe. Materials needed include a balloon, ruler, paper strip, a copy of this page, and a marker.
2. Use the markers to make 10-15 dots on the balloon and number 10 of them after the balloon is partially inflated.
3. Inflate balloon with 4 medium breaths to about the size of your fist; do not over inflate the balloon!
4. Bend the end of the balloon down and paper clip it so that no air escapes.
5. Record what happens to the dots in the space provided below. Be very specific; use complete sentences.
6. Measure and record the distance between dot number one (your "home" dot) and the next 10 other dots with the METRIC RULERS. Be careful not to indent the balloon by pressing on it.
7. Now measure and record the distance between dot number one (your "home" dot) and 10 other dots with the paper strip.
8. Double the size of the ballon by inflating it slowly; do not over inflate the balloon! Measure and record the data from the enlarged balloon using both tools.
9. Answer the summary questions
below.
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Summary Questions
a. If the dots represent galaxies, do they get larger as the balloon (i.e. the universe) expands?
Why do you think this is or is not so?
b. What relationship exists between the speed of the galaxies moving apart and their initial distance from one another?
Name this Principle.
c. Which measuring tool was more accurate?
Why?
d. What is harder for the astronomer to measure: a galaxy's redshift, indicating recessional velocity, or its precise distance from Earth? Why?
Explain your answer.
f.
Astronomers often use Cepheid variables to determine distance. What
is the period of this Cepheid variable in the galaxy called M101
(animated_gif
and digital
image)?
Explain how astronomers use Cepheid variables to determine distance?
Concept Application
The
Space Telescope Science Institute (STSci)
in Baltimore maintains current information and press releases regarding
findings from the Hubble Space Telescope. With a partner, investigate
one
of the many cosmology findings from the HST. Create an electronic
report that describes the HST finding and how it relates to the balloon
activity you just completed.
Classroom Debriefing
Cosmology is the search for origins. It seems as if everyone wants to know how the Universe began. The Big Bang Theory is the result of several important observations. In 1927, Edwin Hubble observed that galaxies are red shifted, and moving farther and farther away from us. Second, he determined that the farther away a galaxy is from Earth, the faster it is receding. If the universe is expanding, then one can assume that the galaxies that compose our universe were once much closer together than they are now. By simply measuring how far apart galaxies are and how fast they are moving, we determine what cosmologists call the Hubble Constant (estimates range from 50 to 100 km/s per kiloparsec). It is very easy to determine the recessional velocity of galaxies; on the other hand, their current positions are difficult to measure. Distances to galaxies are typically measured by finding Cepheid variable stars or supernovae with known brightness. If we run the expansion process backward, we get two results. The first result is that it probably took approximately 15 billion years for the Universe to grow to its present size. Second, some awesome event must have caused the galaxies to go flying away from one another. Scientists don't know exactly what this phenomena could have been, but astronomers refer to it as the Big Bang.
There are four fundamental
observations and inferences that suggest that a Big Bang of some
type did actually occur very long ago.
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| Almost all galaxies are red-shifted | Almost all galaxies are moving away from the Milky Way |
| The most distant galaxies exhibit the greatest red-shift | The most distant galaxies are moving away the fastest |
| The ratio of recessional velocity to distance is between 50 and 100 and is called the Hubble Constant | The Universe has been expanding for 8 to 15 billion years. |
| The Cosmic Background Explorer (COBE) found that the temperature of intergalactic space was not zero | The universe has not yet cooled from the rapid Big Bang expansion. |
| What are some examples that
demonstrate the difference between an observation and an inference?
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The origin of the universe remains one of the greatest questions in science. The "big bang" theory places the origin between 10 and 20 billion years ago, when the universe began in a hot dense state; according to this theory, the universe has been expanding ever since. |