Chap 9

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Chap 9
2013-01-16 21:43:57

Chap 9
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  1. Milky Way
    The galaxy in the universe that contains the solar system; appears as a hazy white band in the night sky.
  2. Galaxy
    A huge collection of stars, planets, gas, and dust held together by gravity.
  3. Star clusters
    A collection of stars held together by gravity
  4. Open clusters
    A collection of 50 − 1000 stars; open clusters appear along the main band of the milky way.
  5. Globular clusters
    A collection of 100 000 to a million stars arranged in a distinctive spherical shape.
  6. Local group
    A small group of about 40 galaxies that include the milky way.
  7. Super clusters
    A gigantic collection of 4 to 25 clusters of galaxies that is hundreds of millions of light-years in size. 
  8. Shapes of galaxies
    • Galaxies have three known classifications.
    • Spiral galaxies, Elliptical galaxies, and Irregular galaxies.The milky way is a spiral.
  9. Cosmology
    The study of the universe.
  10. Doppler effect
    The change in the pitch of a sound due to the motion of the source relative to an observer; also, the change in frequency of a light source due to it motion relative to an observer.
  11. Redshift
    The displacement of spectral lines toward longer wavelengths (the red end of the spectrum) in radiation from distant galaxies and celestial objects.
  12. Blue shift
    The displacement of the spectrum to shorter wavelengths in the lightcoming from distant celestial objects moving toward the observer.
  13. Big Bang
    The explosion of dense matter that, according to currentcosmological theories, marked the origin of the universe.
  14. Cosmic microwave radiation
    The radiation left over from the big bang that fills the universe.
  15. Dark matter
    The most abundant form of matter in the universe; invisible to telescopes.
  16. Dark energy
    A form of energy that makes nearly three quarters of the universe; has the effect  of increasing the expansion of the universe.