In this quick opening, you’ll be introduced to the concept of the Doppler effect. Astronomers’ ability to observe the Doppler effect in distant stars and galaxies has enabled them to better understand the scale and nature of our Universe. You’re not simply going to hear about the Doppler effect; your teacher will demonstrate it.

Listen as your teacher demonstrates the Doppler effect. Can you hear the pitch of the object change as it moves toward and away from you? If not, your teacher may have you move so that you are in line with the direction in which they’re moving the object. What do you notice about the pitch of the sound as it’s moving toward you? How about when it moves away?

Have you ever heard an ambulance siren that seems to change in pitch as it gets closer, and then passes you? These are all examples of the Doppler effect. Sound travels in waves. As an object moves closer, those waves bunch closer together, and we hear the pitch get higher. As the object moves away, the waves get stretched out, and we hear a lower pitch.

Light also travels in waves, and astronomers observe this Doppler effect on stars and entire galaxies, and use it to gather information about the Universe’s greatest mysteries.

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The Universe contains everything, and although it’s expanding, it’s not expanding “into” anything. Two good analogies for thinking about the expanding Universe are a balloon that is being inflated, and a loaf of rising raisin bread. From any point in the Universe, it looks like everything else is moving away, and things that are farthest away are moving the fastest. Whether the Universe is finite or infinite, it has no edge. If we were able to travel long enough in one direction, scientists believe that we would eventually return to our starting place.

Only within the last century have scientists gathered enough data to support the Big Bang theory. Today, astronomers agree that the Universe is expanding. But our three-dimensional human experience doesn’t allow us to easily imagine how that expansion is happening. We need new models and ways to think about how the Universe is expanding.

Preview

What is the Universe expanding into? In this video, Fraser Cain explains that although this is a natural question to ask, it is a question with no answer.

Key Ideas – Factual

Think about the following questions as you watch the video:

1. What is the definition of the Universe?
2. Instead of a spray of matter exploding from a single point, what is a better analogy for the Big Bang?
3. If you were an ant standing on the surface of an expanding balloon, how would other ants on the surface look to you?
4. Why do scientists think that if you could see far enough, you would be able to see the back of your own head?
5. What is another analogy for the expanding Universe? 

Thinking Conceptually

From the standpoint of any ant on an expanding balloon, or any raisin in a rising loaf of raisin bread, all the other ants or raisins are moving away from it. We might conclude that since everything in the Universe seems to be moving away from us, that we are the center of the Universe. Why, then, do scientists say there is no center of the Universe?

In this activity, you will create a model to better understand how the Universe is expanding.

Working in small groups, you’re going to use a balloon to better understand one of the expanding Universe analogies Fraser used in the video you watched. Inflate your group’s balloon until it is about 4 inches (10 cm) in diameter. Have someone in your group pinch the balloon closed with their fingers—don’t tie it off!

Now, have someone else in your group use a felt-tip marker to draw five dots on the balloon, being sure to scatter the dots all over it. Draw gently so you don’t pop the balloon—this is your Universe! Label one dot "MW" and the others “A,” “B,” “C,” and “D.”  “MW” stands for our home in the Milky Way galaxy, and the other letters represent other galaxies in the Universe.

Working together, and without letting air out of the balloon, use the string and ruler to measure the distance from the “MW” dot to each other dot. Have someone in the group record the distances under the Time 1 heading of the table on your Big Bang Balloon Worksheet.

Now, inflate the balloon so that its diameter is about 2 inches (5 cm) bigger. Again, measure the distances from “MW” to each of the dots, and record the distances under Time 2 on the worksheet. Inflate the balloon two more times in 2-inch (5-cm) increments. After each inflation, measure and record the distances on your worksheet.

Once your group has collected all of your data, you can let out the air from your balloon. On your worksheet, write down answers to the following questions, and be prepared to share your answers with the class:

1. What did you notice about the distance from your Milky Way dot to the other galaxy dots as you inflated your balloon?
2. Did any of your groups’ galaxy dots move closer to your Milky Way dot as the balloon inflated?
3. Which dots appeared to move the greatest distance—the ones that started close to the Milky Way, or the ones that started the farthest away?

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Today, the Hubble telescope gathers information that helps us understand the nature of our Universe. Edwin Hubble is credited with determining that there are other galaxies in the Universe beyond our own Milky Way, and for demonstrating that the Universe is expanding at a constant rate.

This video will give you an overview of the work of Edwin Hubble, who studied distant stars and made two important discoveries that helped us understand the tremendous scale and expanding nature of the Universe.

Preview

Before Edwin Hubble’s groundbreaking contributions to astronomy, scientists believed that our Universe was a constant size, and that it was only as large as our galaxy, the Milky Way. Hubble studied individual stars and calculated their distance from Earth. What he discovered changed our understanding of the Universe. Not only are we just one of many galaxies, but the Universe is expanding.

Key Ideas – Factual

Think about the following questions as you watch the video:

1. What is a Cepheid?
2. What did Hubble discover about the size of the Universe from studying the data from the Cepheid star?
3. What further impact did Hubble’s discovery have on our understanding of our relationship to other galaxies within the Universe?
4. What happens to the observed wavelength and color of a galaxy that is moving away from Earth, as opposed to a galaxy moving toward Earth?
5. What is Hubble’s law, in your own words?
6. What theory does Hubble’s law support?
7. What does the Hubble telescope do?

Thinking Conceptually

Think about the balloon activity we did earlier in the lesson. What does Hubble’s law tells us about it?

The Hubble telescope is helping modern astronomers collect information on how dark matter behaves. Although we can’t observe dark matter directly, we can study its effects by studying and comparing photographs that show dark matter’s gravitational pull on surrounding light sources.

This article will give you an overview of some breakthrough images that the Hubble telescope helped us see in 2007. These images helped astronomers begin to describe dark matter, which remains one of the biggest mysteries in modern astronomy.

Skimming for Gist

The Hubble telescope was launched into low orbit in 1990, and has changed the way we think about the Universe. The clear and breathtaking photographs that Hubble takes without obstruction and with different wavelengths of light are simply not achievable from observatories on Earth. In addition to black holes and exoplanets, the Hubble telescope is helping us gather information on one of the biggest mysteries of the Universe—dark matter.

Understanding Content

By the end of the second close read, you should be able to answer the following questions:

1. What do we know about the atoms that make up dark matter?
2. What analogy can we use to describe what happens to dark matter when two galaxy clusters collide?
3. Why is this collision, captured unexpectedly by Hubble astronomers, significant to our understanding of dark matter?
4. How can astronomers study dark matter if they can’t see it?

Thinking Conceptually

Can you think of any other examples of learning about something by studying what we cannot see? 

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Some of the most compelling questions in modern science surround the nature of dark matter and dark energy. What we don’t yet understand about the Universe is inspiring scientists around the world to keep studying it. The empty space we used to think of as “nothing” may turn out to be the most important and powerful energy in the Universe.

This video will give you an overview of dark matter and dark energy.

Preview

All of the things we can observe in this Universe, including planets, stars, and distant galaxies, make up less than 5 percent of the matter in it. So what makes up the rest? Scientists don’t really know, but they know that galaxies would fly apart without dark matter, and that the rate of expansion of the Universe is related to dark energy.

Key Ideas – Factual

Think about the following questions as you watch the video:

1. What percentage of the known Universe is made up of matter that we can see?
2. How do we know that dark matter exists?
3. What are we able to observe near areas where dark matter exists?
4. What do we know is not dark matter?
5. What happens to space in between galaxies as the Universe expands?
6. If the Universe is constantly expanding, why don’t we experience that expansion in our daily lives?
7. How does dark energy relate to empty space?
8. How powerful is dark energy?

Thinking Conceptually

Think about the balloon activity we did earlier in the lesson. What does Hubble’s law tells us about it?

In this activity, you’ll illustrate some of your ideas and questions about the shape of the Universe, dark energy, dark matter, or what you imagine will happen at the “end” of the Universe.

This has been a pretty strange unit—you’ve imagined yourself as an ant and a raisin, you’ve learned that faraway galaxies are racing even farther away, and that less than 5 percent of the Universe is made up of matter that we can see. You’ve already been using your imagination to try to understand these concepts; now you’ll use your imagination to imagine where we’re headed next.

Pick at least one concept from this lesson and incorporate it into a comic strip. Use this space to imagine the shape of the Universe, travel distances to other galaxies, explore dark matter or dark energy, or tell the story of what you think will be the next big breakthrough as we study the cosmos.

Be ready to share your comic strip with the class.