In the 1920's an astronomer named Edwin Hubble began looking at the spectral lines of far away stars. He noticed that they did not match any of the known elements at the time. However, he also noticed that they were parallel to the spectral lines produced by hydrogen, but shifted slightly toward the red. He noticed most of the stars were shifted by a small percent toward the red. He calculated that these galaxies and stars were moving away from Earth at a rate of 1 million meters per second.

As astronomers studied galaxies in the universe more intensely, they noticed that almost all of them were red-shifted, indicating the galaxies were moving farther and farther apart from one another. In other words, the universe is getting bigger!

The expanding universe can be compared to a loaf of raisin bread when it rises before baking. When first mixed, all of the raisins are fairly close together. As it rises, the raisins (representing all the galaxies in the universe) spread out away from one another. Those on the edge spread out faster than those in the center.

This raisin example is similar to how galaxies move away from the center of the universe. Those that are closest to the center of the universe do not move as quickly or as far as the stars and galaxies that are farther from the center of the universe. Because of the Doppler Effect, scientists realize that the shift toward the red part of the spectrum indicates the light source is moving away. If stars or galaxies were moving toward Earth, the shift would be toward the blue part of the spectrum.

Activity: Stellar Objects Under the Red-Shift Drawing

Materials:

• Legal Size Paper
• Colored Pencils

Safety concerns: As with all science lab activities, the most important safety rule is to follow all teacher directions.

Procedure:

1. Get a legal size piece of paper and fold it hamburger style and then, without opening it back up, fold it hot dog style to create four equal columns when you completely unfold the paper.
2. Draw a quarter moon-shaped picture of Earth in the far left column, spanning the length of the paper, starting at the left edge and not covering more than 1⁄2 of the column width.
3. Choose four common stellar objects such as stars, comets, asteroids, space shuttles, or the moon, and draw and color them in the first column, just to the right of Earth.(Important: each object can only be drawn in one color.)
4. Now imagine that each of these objects is moving away from the earth so that each object’s color becomes red-shifted. For each of the remaining columns, change the color of the stellar objects according to the red shift (example: if you draw a green star in the first column, in the next column you would draw it yellow according to the red-shift.)

Analysis:
1. If one of your objects becomes red before the last column of the page, what will happen to it in the next column?
2. What wavelength changes occur as stellar objects expand that cause their true colors to become red shifted?

 Highlight the box below to check your answers! It will disappear because it will leave the visible light spectrum. As the objects move away, the wavelengths that we perceive as color get longer. This causes a shift in color toward the red end of the visible light spectrum.

Review science lab safety rules here.

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1. The title of the activity

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Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE Earth Systems Science core.

Updated October 24, 2008 by: Glen Westbroek