LIFE'S BIG QUESTIONS: How Did the Universe Begin?
At the Keck Observatory in Hawaii, astronomers Sandy Faber and Alan Dressler study stars and galaxies through the largest and most powerful telescope on the planet. Using telescopes as time machines, astronomers hope to understand more about the origins of the universe and the Big Bang theory. Through the lens of the Hubble Space Telescope, astronomers are able to travel back in time to see what the universe might have looked like a few billion years ago. Frontiers takes us along for the view.
Activity 1: Modeling Red Shift
Activity 2: Modeling an Expanded Universe
Activity 3: Find Your Place in the Galaxy
Doppler weather radar,
expansion and contraction of materials
ACTIVITY 1: MODELING RED SHIFT
How do astronomers know that the universe is expanding? One way is by the phenomenon of red shift. When Edwin Hubble, the astronomer for whom the Hubble Space Telescope is named, measured the spectrum of distant stars and galaxies, he observed extra amounts of red light (red shifting).
Red shift occurs when a light-emitting body moves away from us. Light waves traveling in front of a body bunch up as it travels; light waves at the trailing end stretch out. The stretched-out light waves are said to be red shifting. Hubble concluded that the red shift means the stars and galaxies are actually moving away, which led him to develop the theory of an expanding universe.
This simple experiment models the red shifting of a moving star.
- long rubber band
- paper star
- Cut the rubber band so it's no longer a loop.
- Stretch the elastic and secure its ends to sturdy supports (chair rungs will work).
- Mark the elastic into 1 cm lengths.
- Make a mark or place a gummed star in the center of the stretched band. Notice how the wavelength marks are the same distance apart on both sides of the star.
- Grasp the star or center mark and stretch it in the direction of one of the supports.
- What happens to the 1 cm markings?
- How do the distances between marks relate to frequency?
- Considering that this model represents red shift, on which side of the star would the observer on Earth most likely be?
- The marks on one side bunch up, while marks on the other side stretch out.
- The closer together the marks, the higher the frequency. The farther apart the marks, the lower the frequency.
- The side where the marks are stretched.
- The red shifting of stars and galaxies is an example of the Doppler effect. Brainstorm a similar activity to model sound waves.
- Research the actual wavelength of colors. Use string to build a model that illustrates the comparative wave shapes of red, yellow and blue. Build a model that illustrates what happens during the Doppler effect.
- Investigate Doppler radar -- how does it work and why does it make a difference to pilots?
- The Earth spins on its axis, rotates around the sun and revolves in a spiral arm around the Milky Way center. How might each of these movements affect the red shift of distant galaxies?
ACTIVITY 2: MODELING AN EXPANDED UNIVERSE
Galaxies are not only moving away from Earth, but according to many scientists they are also traveling out from the location of the Big Bang.
- To model the expanding universe, you'll need a balloon, ruler and gummed stars. Place the stars on an uninflated balloon in a random pattern. (You may also use a marker to mark "stars" on a balloon instead.) Measure the distance between any five pairs of stars, and record this information. Then inflate the balloon halfway. Remeasure the distance of your selected pairs. Have any of the stars gotten closer? Explain. Inflate the balloon to its fullest capacity. Remeasure the distances. What has changed? Why?
ACTIVITY 3: FIND YOUR PLACE IN THE GALAXY
In this episode of Frontiers, you've seen astronomers working with the Hubble and Keck telescopes to learn more about the universe and the galaxies in it.
Astronomers can calculate the distances between stars, but how do we know where our solar system is in this vast array of stars? In this activity, you represent the solar system. Other students in your classroom represent stars in the "galaxy" (classroom). You will map your place in the galaxy, then see if other students can identify where you are from your map. This exercise will give you practice in three-dimensional mapping. It will also help you understand how astronomers figure out where our solar system lies in relation to other stars.
- Fold a piece of paper into four sections. Open the paper and label the sections "front view," "rear view," "left view," "right view." Seated at your desk, you will make a drawing in each of the four sections that depict what you see in the "galaxy."
Note: In your drawings, students' heads represent stars. Heads that are close will appear larger than heads that are farther away. The apparent sizes should be represented in the diagrams.
- Observe the locations of all the students' heads sitting in front of you. Draw the "front view" by using circles to represent their heads. Draw larger circles for those students who are closer to you and smaller circles for those who are farther away. Some students may be partially or completely hidden from your view.
- Draw the "rear view," showing the heads of students who sit behind you. Then diagram your left and right views.
- On another sheet of paper, draw an overhead view of the pattern of desks in the room. Keep the overhead view. Put an identifying number on your four-view diagram (so you can find it later), then give it to your teacher.
- Your teacher will give you a diagram from an unknown student. Your task is to interpret the diagram to find out where that student is located in the classroom. When you have identified the location of the student who drew the diagram, go back to your overhead view and mark with an X where that person sits. Then, check with the teacher to see if you are right. If not, try again!
Note to the teacher: You may wish to prepare sheets in advance for the student diagrams. Number the sheets so the diagrams can be identified after students exchange them. Students should not know whose diagram they have received.
- Our galaxy is shaped like a disk that bulges in the middle. How do we know that we are located near the edge of our galaxy?
(Because we do not see equal numbers of stars in all directions.)
- How do we know that our galaxy is relatively flat?
(Because we see few stars above and below the main body of our disk-shaped galaxy.)
- Draw diagrams to show how many stars we might see in four different directions.
(Most stars will be visible in one direction or two adjacent directions.)
- How would your diagram be different if our solar system were located in the center of the galaxy?
(There would be an almost equal number of stars seen in each direction.)
- Suppose our galaxy were spherical. Make diagrams to show how many stars we might see if we were located on the edge.
(Most stars will be visible in one direction or two adjacent directions.)
- How would your diagram be different if we were in the center of the spherical galaxy?
(There would be an almost equal number of stars seen in every direction.)
Black holes are regions in space with a small diameter and intense gravitational pull, perhaps caused by the collapse of a star. Some astronomers believe that black holes produce rips in the fabric of time and space, creating entrances to parallel universes. Write a science fiction story about someone who falls into a black hole and emerges in a parallel universe.
Scientific American Frontiers
Fall 1990 to Spring 2000
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