Astronomy Chapter 15

  1. cosmology
    the study of the nature, origin, and evolution of the universe
  2. Olbers's paradox
    the conflict between observations and the theory about why the night sky should or should not be dark
  3. observatble universe
    the part of the universe that we can see from our location in space and time
  4. expanding universe
    A universe that shows an overall increase in distance between galaxies
  5. big bang
    the high-density, high-temperature state from which the expanding universe of galaxies began
  6. Hubble time
    the age of the universe equivalent to 1 divided by the hubble constant
  7. cosmic microwave background radiation
    radiation from the hot clouds of the big bang explosion
  8. antimatter
    matter composed of anti-particles, which upon colliding with a matching particle of normal matter annihilate and convert the mass of both particles into energy
  9. recombination
    the stage within 300,000 years of the big bang, when the gas became transparent to radiation
  10. dark age
    the period of time after the glow of the big bang faded into the infrared and before the birght of the first stars, during which the universe expanded into darkness
  11. reionization
    the stage in the early history of the universe when ultraviolet photons form the first stars ionized the gas filling space
  12. isotropy
    the assumption that in its general properties the universe looks the same in every direction
  13. homogeneity
    the assumption that, on the large scale, matter is uniformly spread through the universe
  14. cosmological principle
    the assumption that any observer in the universe sees the same general features of the universe
  15. critical density
    the average density of the universe needed to make its curvature flat
  16. closed universe
    a model of the universe in which the average density is great enough to stop the expansion and make the universe contract
  17. flat universe
    a model of the universe in which space-time is not curved
  18. open universe
    a model of the universe in which the average density is less than the critical density needed to halt the expansion
  19. nonbaryonic matter
    proposed dark matter made up of the particles other than protons and neutrons
  20. hot dark matter
    dark matter made up of the particles such as neutrinos traveling at or nearly at the speed of light
  21. cold dark matter
    mass in the universe, as yet undetected except for its gravitational influence, which is made up of slow-moving particles
  22. flatness problem
    in cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat
  23. horizon problem
    • in cosmology, the circumstance that the primordial background
    • radiation seems much more isotropic than can be explained by the standard big band theory
  24. inflationary universe
    a versino of the big bang theory that includes a rapid expansion when the universe was very young; derived from grand unified theories
  25. grand unified theories (GUTs)
    theories that attempt to describe in a smiliar way the electromagnetic, weak, and strong forces of nature
  26. quintessence
    postulated energy that fills empty space and drives the accelerationg of the universe; also known as dark energy
  27. dark energy
    the energy believed to fill empty spaces and drive the acceleration of the expanding universe; also known as quintessence
  28. large-scale structure
    the distribution of clusters and superclusters of galaxzies in filaments and wall enclosing voids
  29. supercluster
    a cluster of galaxy clusters
  30. filaments
    long strands of superclusters of galaxies that surround voids that produce the large-scale structure of the universe
  31. voids
    areas that are nearly empty of galaxies in between filaments that produce the large-scale structure of the universe
Card Set
Astronomy Chapter 15
Cosmology- key terms and concepts