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| In 1929, astronomer Edwin Hubble showed that our universe was expanding, providing the first evidence for the Big Bang Theory. He had previously shown that the Milky Way was not the entire universe, but one of millions of galaxies. In the next few activities, we will explore the evidence for galaxies moving away from us and discuss Hubble's law. |
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| ACTIVITIES on the Doppler Effect and Redshift Most of you have heard the change in pitch as a police car with its siren going approaches and then passes you. If you need a refresher, try the Doppler apparatus (a tuning fork on a string) in the classroom. Strike the tuning fork and then swing it in a horizontal circle over your head. How does the pitch change as the tuning fork approaches you? As it moves away from you? Sound, like light, travels in waves. The wavelengths of the sound are changed if the source making them is moving towards or away from you. This stretching or compression of wavelength is known as the Doppler effect. Light or electromagnetic radiation also experiences the Doppler effect which is observed as redshift or blueshift. Hubble noticed that the spectra of galaxies were not only redshifted, but that the amount of redshift increased with the distance of the galaxy. This led him to believe that the galaxies were moving away from us. |
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 Chandra Data and the Doppler EffectA series of activities illustrating the Doppler effect with examples from the Chandra X-ray Observatory. Teachers may email P. Perry for answer key. The Doppler EffectGreat tutorial and online lab, but no longer free! Included in Brooks/Cole "Virtual Astronomy" Here is an alternate Doppler activity. |
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| ACTIVITIES on Hubble's Law |
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The Expanding Universe In this exercise, you will use a two-dimensional analogy to explore the expansion of the Universe.
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| The Cepheid Yardstick How could Hubble and other astronomers determine the distances to galaxies much too far for parallax measurements? This exercise discusses how a star called a Cepheid variable is used for distance measurements. Here is an alternate activity: The Distance to M81 using Cepheids. |
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| Measuring Distance In Hands-On Universe Book 6, do "Determining Distance or Luminosity Using Apparent Brightness" (p. 16-18) and "Cepheid Variable Stars as Distance Indicators" (p. 19-24). You will be using image processing software to manipulate actual images containing Cepheid variables. |
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| Cosmology Read up to the section review and answer the questions in Strobel's Astronomy Notes. |
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