Astronomy Chapter 12

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Astronomy Chapter 12
2012-04-17 21:36:31
ASTR 205

Our Galaxy: The Milky Way- Key terms of concepts
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  1. variable star
    a star whose brightness changed periodically
  2. Cepheid variable star
    • variable star with a period of up to 60 days.
    • the period of variation is related to lumionsity
  3. instability strip
    the region of the H-R diagram in which stars are unstable to pulsation. A star passing through this strip becomes a variable star
  4. RR Lyrae variable star
    variable star with a period of from 12-24 hours. Common in some globular clusters
  5. Period-luminosity relation
    the relation between period of pulsation and intrinsic brightness among Cepheid variable stars
  6. proper motion
    the rate at which a star moves across the sky. This rate is measured in seconds of arc per year
  7. calibrated
    the establishment of the relationship between a parameter that is easily determined and a parameter that is more difficult to determine
  8. disk component
    all material confined to the plane of the galaxy
  9. kiloparsec
    a unit of distance equal to 1000 pc or 3260 ly
  10. spiral arm
    long spiral pattern of bright stars, star clusters, gas and dust that extend from the center to the edge of the disk of spiral galaxies
  11. spherical component
    the part of the galaxy including all matter in a spherical distibution around the center (the halo and nuclear bulge)
  12. halo
    the spherical region of a spiral galaxy, containing a thin scattering of stars, globular star clusters, and small amounts of gas
  13. nuclear bulge
    the spherical cloud of stars that lies at the center of spiral galaxies
  14. rotation curve
    a graph of orbital velocity versus radius in the disk of a galaxy
  15. dark halo
    the low-density extension of the halo of our galaxy believed to be composed of dark matter; also called the galactic corona
  16. galactic corona
    the extended, spherical distribution of the low-luminosity matter believed to surround the Milky Way and the other galaxies; also called the dark halo.
  17. dark matter
    nonluminous matter that is detected only by its gravitational influence
  18. population I
    stars rich in atoms heavier than helium. Nearly always relatively young stars found in the disk of the galaxy
  19. population II
    stars poor in atoms heavier than helium
  20. metal
    in astronomical usage, all atoms heavier than helium
  21. spiral tracer
    a celestial object used to map spiral arms.
  22. density wave theory
    theory proposed to account for spiral arms as compressions of the interstellar medium in the disk of the galaxy
  23. self-sustaining star formation
    the process by which the birth of stars compresses the surrounding gas clouds and triggers the formation of more stars