Astronomy Chapter 9

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Astronomy Chapter 9
2012-04-17 20:40:38
ASTR 205

Stellar Births- key terms and concepts
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  1. interstellar medium
    the dust and gas distributed between the stars
  2. nebula
    a glowing cloud of gas or a cloud of dust reflecting or obscuring the light of nearby stars
  3. interstellar reddening
    the process in which dust scatters blue light out of starlight andm akes the stars look redder
  4. interstellar dust
    microscopic solid grains in the interstellar medium
  5. emission nebula
    a cloud of glowing gas excited by ultraviolet radiation from hot stars
  6. HII region
    a region of ionized hydrogen around a hot star
  7. reflection nebula
    a nebula produced by starlight reflecting off dust particles in the interstellar medium
  8. dark nebula
    a cloud of gas and dust of any size seen silhouetted against a brighter nebula or star field
  9. interstellar absortion lines
    narrow spectral lines produced as starlight travels through the thin gas of the interstellar medium
  10. molecular cloud
    a dense interstellar gas cloud in which atoms are able to link together to form molecules such as H2 and CO
  11. shockwave
    a sudden change in pressure that travels as an intense sound wave
  12. star cluster
    stars held together in a stable group by their combined gravity
  13. association
    group of widely scattered stars moving together through space
  14. protostar
    a collapsing cloud of gas and dust destined to become a star
  15. evolutionary track
    a path star follow on the H-R diagram as it gradually changed its surface temperature and luminosity
  16. CNO cycle
    a series of nuclear reactions that use carbon as a catalyst to combine four hydrogen atoms to make one helium atoms plus energy
  17. triple-alpha process
    the nuclear fusion process that combines three helium nuclei the make on carbon nucleus
  18. conservation mass
    one of the basic laws of stellar structure that states the total mass of the star must equal the sum of the masses of the shells
  19. conservation of energy
    one of the basic laws of stellar structure that states the amount of energy flowing out of the top of a shell must equal the amount cmoing in at the bottom plus whatever energy is generated within the shell
  20. hydrostatic equilibrium
    the balance between the weight of the material pressing downward on alayer in a star and the pressure in that layer
  21. stellar model
    a table of numbers representing the conditions in various layers within a star
  22. brown dwarf
    a star whose mass is too low to ignite nuclear fusion
  23. zero-age main sequence (ZAMS)
    the location of the H-R diagram where stars first reach stability as hydrogen-burning star
  24. pressure-temperature thermostat
    the relation between gas pressure and temperature, the stability of a star depends upon this