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27 Cards in this Set

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association
Group of widely scattered stars (10 to 100) moving together through space. Not gravitationally bound into clusters. (p. 180)
brown dwarf
A star whose mass is too low to ignite nuclear fusion. Heated by contraction. (p. 192)
carbon-nitrogen-oxygen (CNO) cycle
A series of nuclear reactions that use carbon as a catalyst to combine four hydrogen atoms to make one helium atom plus energy. Effective in stars more massive than the sun. (p. 183)
CNO cycle
See carbon-nitrogen-oxygen cycle.
conservation of energy
One of the basic laws of stellar structure. The amount of energy flowing out of the top of a shell must equal the amount coming in at the bottom plus whatever energy is generated within the shell. (p. 187)
conservation of mass
One of the basic laws of stellar structure. The total mass of the star must equal the sum of the masses of the shells, and the mass must be distributed smoothly through the star. (p. 187)
dark nebula
A cloud of gas and dust seen silhouetted against a brighter nebula. (p. 177)
emission nebula
A cloud of glowing gas excited by ultraviolet radiation from hot stars. (p. 176)
energy transport
Flow of energy from hot regions to cooler regions by one of three methods: conduction, convection, or radiation. (p. 188)
evolutionary track
The path a star follows in the H-R diagram as it gradually changes its surface temperature and luminosity. (p. 180)
H II region
A region of ionized hydrogen around a hot star. (p. 176)
Herbig-Haro object
A small nebula that varies irregularly in brightness. Believed to be associated with star formation. (p. 185)
hydrostatic equilibrium
The balance between the weight of the material pressing downward on a layer in a star and the pressure in that layer. (p. 187)
infrared cirrus
Wispy network of cold dust clouds discovered by the Infrared Astronomy Satellite. (p. 178)
interstellar dust
Microscopic solid grains in the interstellar medium. (p. 174)
interstellar medium
The gas and dust distributed between the stars. (p. 174)
interstellar reddening
The process in which dust scatters blue light out of starlight and makes the stars look redder. (p. 174)
molecular cloud
A dense interstellar gas cloud in which atoms are able to link together to form molecules such as H2 and CO. (p. 179)
nebula
A glowing cloud of gas or a cloud of dust reflecting the light of nearby stars. (p. 175)
opacity
The resistance of a gas to the passage of radiation. (p. 189)
protostar
A collapsing cloud of gas and dust destined to become a star. (p. 180)
reflection nebula
A nebula produced by starlight reflecting off dust particles in the interstellar medium. (p. 176)
shock wave
A sudden change in pressure that travels as an intense sound wave. (p. 179)
stellar model
A table of numbers representing the conditions in various layers within a star. (p. 189)
T Tauri star
A young star surrounded by gas and dust. Believed to be contracting toward the main sequence. (p. 184)
triple-alpha process
The nuclear fusion process that combines three helium nuclei (alpha particles) to make one carbon nucleus. (p. 186)
zero-age main sequence (ZAMS)
The location in the H-R diagram where stars first reach stability as hydrogen-burning stars. (p. 193)