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Ch23 - Assignment Chapter 23 Class Astronomy I Date...

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Assignment: Chapter 23 Class: Astronomy I Date: November 19th, 2007 Review Questions 1. Because Milky Way completely encircles us, all the stars in the sky are part of an enormous disk of stars, and we see them as a bright band. 2. Interstellar extinction only allowed us to see the nearest stars in the Galaxy. Hence, we had no idea of either the enormous size of the Galaxy or of the vast number of stars concentrated around the center. 3. Because globular clusters are located above the Galactic plane, we were still able to see them through interstellar dust. 4. RR Lyrae variables are very similar to the Cepheid variables, but these have shorter pulsation periods and lower peak luminosities. Since these are so commonly found in glublar clusters, Shapley was able to determine the distances to the globular clusters using period-luminosity relationship. 5. The longer the wavelength, the farther radiation can travel through interstellar dust without being scattered or absorbed. Hence, infrared radiation can traverse the Galaxy freely. 6. The stars in the disk are mostly young, metal-rich, Population I stars like the Sun. The presence of these astronomically young stars shows that there must be active star formation in the galactic disk. 7. No O and B stars are present in the halo, because star formation ceased there long ago. 8. When the spin of the electron changes its orientation from the high-energy to low- energy, this spin-flip transition emits 21-cm radio emission.
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